UVa 10347

#include <bits/stdc++.h>
// #include <iostream>
// #include <cstdio>
// #include <cstdlib>
// #include <algorithm>
// #include <cmath>
// #include <vector>
// #include <set>
// #include <map>
// #include <queue>
// #include <stack>
// #include <ctime>
// #include <cassert>
// #include <complex>
// #include <string>
// #include <cstring>
// #include <bitset>
using namespace std;

// #pragma GCC optimize("Ofast,no-stack-protector")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC optimize("unroll-loops")

#define ll              long long int
#define vi              vector< int >
#define vll             vector< ll >

#define sc              scanf
#define pf              printf
#define cspf(i)         pf("Case %d: ", i)
#define spc             pf(" ")
#define line            pf("\n")

#define ff              first
#define ss              second
#define mp              make_pair
#define pb              push_back
#define ppb             pop_back
#define tp(v,j)         get<j>(v)
#define Log(b,x)        (log(x)/log(b))

#define FOR(i,x,y)      for(int i = int(x); i < int(y); i++)
#define ROF(i,x,y)      for(int i = int(x)-1; i >= int(y); i--)
#define clr(arr,x)      memset(arr, x, sizeof arr)
#define vout(v,sz)      for(int w=0;w<sz;w++){if(w) spc; cout<<v[w];}
#define all(v)          v.begin(), v.end()
#define rall(v)         v.rbegin(), v.rend()
#define unq(v)          sort(all(v)),(v).resize(unique(all(v))-v.begin())
#define fastIO          ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr)

#define sc1(x)          sc("%d",&x);
#define sc2(x,y)        sc("%d %d", &x, &y)
#define sc3(x,y,z)      sc("%d %d %d", &x, &y, &z)
#define scl1(x)         sc("%lld",&x);
#define scl2(x,y)       sc("%lld %lld", &x, &y)
#define scf1(x)         sc("%lf",&x);
#define scf2(x,y)       sc("%lf %lf", &x, &y)

#define pf1(x)          pf("%d",x);
#define pf2(x,y)        pf("%d %d", x, y)
#define pfl1(x)         pf("%lld",x);
#define pfl2(x,y)       pf("%lld %lld", x, y)

#define MOD             (int)(998244353)
#define MaxN            100000
#define inf             0x3f3f3f3f
#define PI              acos(-1.0)  // 3.1415926535897932
#define eps             1e-6

template <class T> inline T bigMod(T p,T e,T M){T ret=1; for(;e>0;e>>=1){ if(e&1) ret=(ret*p)%M; p=(p*p)%M;} return (T)ret;}
template <class T> inline T modInverse(T a,T M){return bigMod(a,M-2,M);}
template <class T> inline T gcd(T a,T b){if(b==0)return a;return gcd(b,a%b);}
template <class T> inline T lcm(T a,T b) {a=abs(a);b=abs(b); return (a/gcd(a,b))*b;}

int dx[] = { 1,-1, 0, 0};                //graph moves
int dy[] = { 0, 0, 1,-1};               //graph moves

struct PT{
    double x,y;
    void scan(){ scanf("%lf %lf",&x,&y);}
    void prnt(){ printf("%.2lf %.2lf\n",x,y);}
};

double SQ(double x){ return x*x;}

double Dis(PT a,PT b){ return SQ(a.x-b.x) + SQ(a.y-b.y);}

double absDis(PT a,PT b){ return sqrt(Dis(a,b));}

double Dot(PT a,PT b){ return a.x*b.x + a.y*b.y;}

double Cross(PT a,PT b){ return a.x*b.y - b.x*a.y;}

double toRadian(double x){ return (x*(PI/180.0));}

double toDegree(double x){ return (x*(180.0/PI));}

//can be represent as a line
PT vect(PT a,PT b){ return {a.x-b.x, a.y-b.y};}

int orientation(PT a,PT b,PT c)
{
    return (b.y-a.y)*(c.x-b.x)-(b.x-a.x)*(c.y-b.y);
}

bool ifParrallel(PT a,PT b,PT c,PT d)
{
    if(abs(Cross(vect(a,b),vect(c,d)))>eps) //line ab and line cd is parrallel if abXcd=0
        return false;
    return true;
}

bool ifPerpendicular(PT a,PT b,PT c,PT d)
{
    if(abs(Dot(vect(a,b),vect(c,d)))>eps) //line ab and line cd is parrallel if ab.cd=0
        return false;
    return true;
}

double heronTriangle(double a, double b, double c){
    double s = (a + b + c) / 2.0;
    if(s - a <= 0) return -1;
    if(s - b <= 0) return -1;
    if(s - c <= 0) return -1;
    return sqrt(s * (s - a) * (s - b) * (s - c));
}

double mdedianTriangle(double a, double b, double c){
    double s = (a + b + c) / 2.0;
    if(s - a <= 0) return -1;
    if(s - b <= 0) return -1;
    if(s - c <= 0) return -1;
    return (4.0 / 3.0 ) * sqrt(s * (s - a) * (s - b) * (s - c));
}

double CircumcircleR(double a, double b, double c){
    return (a * b * c) / sqrt((a + b + c) * (b + c - a) * (c + a - b) * (a + b - c));
}

double IncircleR(double a, double b, double c){
    return 2.0 * heronTriangle(a, b, c) / (a + b + c);
}

///Area of irregular polygon
double AreaOfPolygon(int n,PT a[])
{
    double area = 0.0;
    for(int i=1;i<n;i++){
        area+=(a[i-1].x*a[i].y-a[i].x*a[i-1].y);
    }
    area+=(a[n-1].x*a[0].y-a[0].x*a[n-1].y);
    return area/2.0;
}

PT f; //init first coordinate
//for clockwise sorting
bool ClockCmp(PT &a,PT &b){ return (f.x-a.x)*(f.y-b.y)<(f.x-b.x)*(f.y-a.y);}

//for anti-clockwise sorting
bool AClockCmp(PT &a,PT &b){ return (f.x-a.x)*(f.y-b.y)>(f.x-b.x)*(f.y-a.y);}

int main()
{
    #ifndef ONLINE_JUDGE
        clock_t tStart = clock();
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif

    double a, b, c;

    while(cin >> a >> b >> c){
        double area = mdedianTriangle(a, b, c);
        pf("%.3lf\n", area);
    }


    #ifndef ONLINE_JUDGE
        fprintf(stderr, "\n>> Runtime: %.10fs\n", (double) (clock() - tStart) / CLOCKS_PER_SEC);
    #endif

    return 0;
}