#include <bits/stdc++.h>
using namespace std;
int main(void) {
  double x[4], y[4];
  while (scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf", x, y, x + 1, y + 1, x + 2,
               y + 2, x + 3, y + 3) != EOF) {
    bool convex = false;
    for (int i = 0; i < 3; i++) {
      double x1, y1, x2, y2;
      x1 = x[i + 1] - x[i];
      y1 = y[i + 1] - y[i];
      x2 = x[(i + 2) % 4] - x[i + 1];
      y2 = y[(i + 2) % 4] - x[i + 1];
      double a, b;
      a = sqrt(x1 * x1 + y1 * y1);
      b = sqrt(x2 * x2 + y2 * y2);
      double sin = (x1 * y2 - x2 * y1) / (a * b);
      if (sin < 0) {
        convex = true;
        break;
      }
    }
    if (convex)
      cout << "NO" << endl;
    else
      cout << "YES" << endl;
  }
  return 0;
}
