UVa 10763

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

typedef long long int           ll;
typedef unsigned long long int  ull;
typedef vector<int>             vi;
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)-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)
/// Constants
#define eps                     1e-9
#define PI                      acos(-1.0)  // 3.1415926535897932

int main()
{
    int t;
    while(1){
        cin>>t;
        if(t==0)
            break;
        vi vf,vs;
        loop(i,t){
            int x,y;
            cin>>x>>y;
            vf.pb(x);
            vs.pb(y);
        }
        sort(vf.begin(),vf.end());
        sort(vs.begin(),vs.end());
        int cnt=0;
        loop(i,t){
            if(vf[i]!=vs[i]){
                cnt++;
                break;
            }
        }
        if(cnt==0)
            printf("YES\n");
        else
            printf("NO\n");
        vf.clear();
        vs.clear();
    }
    return 0;
}