#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() {
  while (1) {
    P p[4];
    char c;
    for (int i = 0; i < 4; i++) {
      if (i != 0) cin >> c;
      cin >> p[i].x >> c >> p[i].y;
      if (cin.eof()) return 0;
    }
    int f = 0;
    for (int i = 2; i < 6; i++) {
      if (det(p[(i - 2) % 4], p[(i - 1) % 4], p[i % 4]) < 0.0) {
        cout << "NO" << endl;
        f = 1;
        break;
      }
    }
    if (f == 0) cout << "YES" << endl;
  }
  return 0;
}
