#include<bits/stdc++.h>
using namespace std;

typedef long long int           ll;
typedef unsigned long long int  ull;
typedef vector<int>             vi;
typedef vector<ll>              vll;
typedef vector<vi>              vvi;
typedef pair<int,int>           pii;
typedef vector< pii >           vpii;
typedef set<int>                sti;

#define pb                      push_back
#define pob                     pop_back
#define mp                      make_pair
#define ff                      first
#define ss                      second
#define loop1(i,n)              for(int i=1; i<int(n); i++)
#define loop(i,y)               for(int i=0; i<int(y); i++)
#define rloop(i,y)              for(int i=int(y); i>0; i--)
#define rloop1(i,y)             for(int i=int(y)-1; i>=0; i--)
#define read()                  freopen("input.txt", "r", stdin)
#define write()                 freopen("output.txt", "w", stdout)
#define cspf(i)                 printf("Case %d: ", i)
#define all(v)                  v.begin(),v.end()
/// Constants
#define eps                     1e-9
#define PI                      acos(-1.0)  // 3.1415926535897932

int main()
{
    vi vt;
    int n;
    char a[100009];
    cin>>n>>a;
    int gcnt=0,tcnt=0,mx=0,x;
    loop(i,n){
        if(a[i]=='G'){
            gcnt++;
            tcnt++;
            continue;
        }
        vt.pb(tcnt);
        tcnt=0;
    }
    vt.pb(tcnt);
    vt.pb(0);
    int sz=vt.size();
    loop1(i,sz){
        x=vt[i]+vt[i-1];
        if(x>mx)
            mx=x;
    }
    if(gcnt>mx)
        mx++;
    cout<<mx<<endl;
    return 0;
}