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

#define EPS (1e-10)
#define equals(a,b) (fabs((a)-(b))<EPS)
#define dle(a,b) (equals(a,b) || a<b)
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; }

  bool operator< ( const Point &p ) const {
    return x != p.x ? x < p.x : y < p.y;
  }
  
  bool operator== (const Point &p) const {
    return fabs(x-p.x) < EPS && fabs(y-p.y) < EPS;
  }
};

typedef Point Vector;

double norm( Vector a ) { return a.x*a.x + a.y*a.y; }
double abs( Vector a ) { return sqrt(norm(a)); }
Point polar( double a, double r ) { return Point(cos(r)*a, sin(r)*a); }
double getDist( Vector a, Vector b ) { return abs(a - b); }
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; }

static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

int ccw( Point p0, Point p1, Point p2 ) {
  // about CCW
  // http://gihyo.jp/dev/serial/01/geometry/0006?page=2

  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( Point P[4] ) {
  int c = ccw(P[0], P[1], P[2]);
  for( int i = 1; i < 4; i++) {
    if( c!= ccw(P[i], P[(i+1)%4], P[(i+2)%4]) ) return false;
  }
  return true;
}

int main() {
  char ch;
  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;
}