#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <string>
#include <cctype>
#include<cmath>
using namespace std;

typedef pair<long long,long long> PII;

int N;
PII V[40500];

long long cross(PII start, PII b1, PII b2){
    PII v1 = make_pair( b1.first - start.first, b1.second - start.second);
    PII v2 = make_pair( b2.first - start.first, b2.second - start.second);
    return v1.first*v2.second - v2.first*v1.second;
}

double sq(double a){ return a*a;}

double dist(PII a, PII b){
    return sqrt( sq(a.first - b.first) + sq(a.second - b.second));
}

bool patri(PII u1, PII u2, PII bod){
    if (cross(u1,u2,bod) != 0) return false;
    return dist(u1,bod) < dist(u1,u2);
}

bool inter(PII u1, PII u2, PII v1, PII v2){
    if (patri(u1,u2,v1) || patri(u1,u2,v2) || patri(v1,v2,u1) || patri(v1,v2,u2)) return true;
    if (cross(u1,u2,v2) * cross(u1,u2,v1) < 0 && cross(v1,v2,u1)*cross(v1,v2,u2) < 0) return true;
    return false;
}

int main(){
    while(true){
        scanf("%d ",&N);
        if (N==0)break;
        for(int i=0;i<N;i++) scanf("%lld %lld ",&V[i].first,&V[i].second);
        bool self = false;
        for(int i=0;i<N;i++){
            for(int j=i+2;j<N;j++){
                if (i==0 && j == N-1)continue;
                if (inter(V[i],V[(i+1)%N],V[j],V[(j+1)%N])) self = true;
                if (self) break;
            }
            if (self) break;
        }

        if (self) printf("NO\n");
        else printf("YES\n");

    }

    return 0;
}