#include <bits/stdc++.h>
using namespace std;
int main() {
  float xa, ya, xb, yb, xc, yc, xd, yd;
  while (scanf("%f,%f,%f,%f,%f,%f,%f,%f", &xa, &ya, &xb, &yb, &xc, &yc, &xd,
               &yd) != EOF) {
    float x[4] = {xa, xb, xc, xd};
    float y[4] = {ya, yb, yc, yd};
    float s[4];
    bool allp = true, alln = true;
    for (int i = 0; i < 4; ++i) {
      s[i] = (x[(i + 1) % 4] - x[i]) * (y[(i + 2) % 4] - y[(i + 1) % 4]) -
             (x[(i + 2) % 4] - x[(i + 1) % 4]) * (y[(i + 1) % 4] - y[i]);
    }
    for (int i = 0; i < 4; ++i) {
      if (s[i] < 0) {
        allp = false;
        break;
      }
    }
    for (int i = 0; i < 4; ++i) {
      if (s[i] > 0) {
        alln = false;
        break;
      }
    }
    if (allp || alln) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  return 0;
}
