#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

// !!! EPS は 1e-10 !!!
#define EPS (1e-10)
static const double PI = M_PI;
 
class Point {
public:
  double x,y;
   
  Point (double x=0, double y=0): x(x), y(y) {}
 
  Point operator+ ( Point p ) { return Point(x+p.x, y+p.y); }
  Point operator- ( Point p ) { return Point(x-p.x, y-p.y); }
  Point operator* ( double k ) { return Point(k*x, k*y); }
  Point operator/ ( double k ) { return Point(x/k, y/k); }
 
  double abs() { return sqrt(norm()); }
  double norm() { return x*x+y*y; }
};
 
typedef Point Vector;
 
double norm( Vector a ) { return a.x*a.x + a.y*a.y; }
double abs( Vector a ) { return sqrt(norm(a)); }
double dot( Vector a, Vector b ) { return a.x*b.x + a.y*b.y; }
double cross( Vector a, Vector b ) { return a.x*b.y - a.y*b.x; }
 
enum { COUNTER_CLOCKWISE, CLOCKWISE, ONLINE_BACK, ONLINE_FRONT, ON_SEGMENT };
 
int ccw( Point p0, Point p1, Point p2 ) {
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if( cross(a, b) > EPS ) return COUNTER_CLOCKWISE;
  if( cross(a, b) < -EPS ) return CLOCKWISE;
  if( dot(a, b) < -EPS ) return ONLINE_BACK;
  if( norm(a) < norm(b) ) return ONLINE_FRONT;
  return ON_SEGMENT;
}
 
bool isConvex(vector<Point> P) {
  int N = P.size();
  if(P.size() < 3) return false; // 三角形を作れないなら false を返す
  int c = ccw(P[0], P[1], P[2]);
  for(int i=1; i<N; i++) {
    if( c != ccw(P[i], P[(i+1)%N], P[(i+2)%N]) ) return false;
  }
  return true;
}
 
int main() {
  char ch;
  vector<Point> P(4);
 
  while(cin >> P[0].x >> ch >> P[0].y ) {
    for(int i=1; i<4; i++) cin >> ch >> P[i].x >> ch >> P[i].y;
    if( isConvex(P) ) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
   
  return 0;
}