#include <bits/stdc++.h>
using namespace std;
const int N = 4;
int main() {
  complex<double> v[N + 2];
  double x[N], y[N];
  char t;
  while (cin >> x[0] >> t >> y[0] >> t >> x[1] >> t >> y[1] >> t >> x[2] >> t >>
         y[2] >> t >> x[3] >> t >> y[3]) {
    for (int i = 0; i < N; i++) v[i] = complex<double>(x[i], y[i]);
    v[N] = v[0];
    v[N + 1] = v[1];
    double ang[N + 2];
    for (int i = 1; i <= 4; i++) {
      ang[i] = fmod(arg(v[i - 1] - v[i]) - arg(v[i + 1] - v[i]) + 10 * M_PI,
                    M_PI * 2);
    }
    int ans = 1;
    if (ang[1] > M_PI) {
      for (int i = 0; i < 4; i++)
        if (ang[i + 1] < M_PI) ans = 0;
    } else {
      for (int i = 0; i < 4; i++)
        if (ang[i + 1] > M_PI) ans = 0;
    }
    if (ans)
      cout << "yes" << endl;
    else
      cout << "no" << endl;
  }
  return 0;
}
