#include <bits/stdc++.h>
using namespace std;
int getRotType(double angle_a, double angle_b) {
  const int eps = 1e-8;
  const double PAI = 3.14159265358979;
  if (fabs(angle_a - angle_b) <= eps) return 0;
  if (angle_a > angle_b + PAI)
    angle_b += 2 * PAI;
  else if (angle_b > angle_a + PAI)
    angle_a += 2 * PAI;
  if (angle_b > angle_a) return 1;
  return -1;
}
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])) {
    double ang[4];
    for (int i = 0; i < 4; i++)
      ang[i] = atan2(y[(i + 1) % 4] - y[i % 4], x[(i + 1) % 4] - x[i % 4]);
    double angType[4];
    for (int i = 0; i < 4; i++)
      angType[i] = getRotType(ang[i], ang[(i + 1) % 4]);
    int i;
    for (i = 0; i < 3; i++) {
      if (angType[i] != angType[i + 1]) break;
    }
    if (i == 3)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}
