#include <bits/stdc++.h>
using namespace std;
int main() {
  const double PI = acos(-1);
  double x[4], y[4];
  complex<double> z[4];
  char c;
  while (cin >> x[0] >> c >> y[0] >> c >> x[1] >> c >> y[1] >> c >> x[2] >> c >>
         y[2] >> c >> x[3] >> c >> y[3]) {
    for (int i = 0; i < 4; i++) {
      z[i].real(x[i]);
      z[i].imag(y[i]);
    }
    bool f = 1;
    for (int i = 0; i < 4; i++) {
      int j = (i + 1) % 4, k = (i + 2) % 4;
      double t = arg((z[k] - z[j]) / (z[j] - z[i]));
      if (!(t > 0 && t < PI)) {
        f = 0;
        break;
      }
    }
    if (f)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
