#include <iostream>
#include <cmath>
using namespace std;
struct P{
  double x,y;
  P(){}
  P(double x,double y):x(x),y(y){}
  P operator - (P p){
    return P(x - p.x,y - p.y);
  }
  double det(P p){
    return x*p.y - y*p.x;
  }
};
int main(){
  P a[4];
  char e;
  while( cin >> a[0].x >> e >> a[0].y){
    int flag = 1;
    for(int i = 1 ; i < 4 ; i++ ){
      cin >> e >> a[i].x >> e >>  a[i].y;
    }
    for(int i = 0 ; i < 4 ; i++ ){
      if((a[(i + 1)%4] - a[i]).det( a[(i + 2)%4] - a[(i + 1)%4] ) <= 0){
	cout << "NO" << endl;
	flag = 0;
	break;
      }
    }
    if(flag)cout << "YES" << endl;
  }
}