#include <bits/stdc++.h>
using namespace std;
vector<pair<int, int> > vec;
int main() {
  double x[4], y[4];
  while (scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf", &x[0], &y[0], &x[1], &y[1],
               &x[2], &y[2], &x[3], &y[3]) != EOF) {
    int suc = 1;
    for (int i = 0; i < 4; i++) {
      if ((x[i] * y[(i + 1) % 4] - y[i] * x[(i + 1) % 4]) *
              (x[(i + 1) % 4] * y[(i + 2) % 4] -
               y[(i + 1) % 4] * x[(i + 2) % 4]) <=
          0) {
        suc = 0;
        break;
      }
    }
    if (suc)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
