#include <bits/stdc++.h>
using namespace std;
struct P {
  double x, y;
};
double det(P& p, P& q, P& r) {
  return (q.x - p.x) * (r.y - q.y) - (q.y - p.y) * (r.x - q.x);
}
int main() {
  P p[4];
  char c;
  while (cin >> p[0].x >> c >> p[0].y) {
    for (int i = 1; i < 4; i++) {
      cin >> c >> p[i].x >> c >> p[i].y;
    }
    int f = 0;
    for (int i = 0; i < 4; i++) {
      if (det(p[i % 4], p[(i + 1) % 4], p[(i + 2) % 4]) <= 0.0) {
        cout << "NO" << endl;
        f = 1;
        break;
      }
    }
    if (f == 0) cout << "YES" << endl;
  }
  return 0;
}
