#include <bits/stdc++.h>
using namespace std;
int main() {
  array<double, 4> x;
  array<double, 4> y;
  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]) {
    array<double, 2> vx;
    array<double, 2> vy;
    bool convex = true;
    for (int i = 0; i < 4; ++i) {
      vx[0] = x[(i + 2) % 4] - x[(i + 1) % 4];
      vy[0] = y[(i + 2) % 4] - y[(i + 1) % 4];
      vx[1] = x[i % 4] - x[(i + 1) % 4];
      vy[1] = y[i % 4] - y[(i + 1) % 4];
      if ((vx[0] * vy[1] - vx[1] * vy[0]) < 0) {
        convex = false;
        break;
      }
    }
    if (convex)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
