#include <bits/stdc++.h>
using namespace std;
//define
#define int long long
#define UNIQUE(v) v.erase(unique(all(v)), v.end());
#define ZIP(v) sort(all(v)),UNIQUE(v)
#define ADD(a, b) a = (a + b) % mod
#define SUB(a, b) a = (a+mod-b)%mod
#define MUL(a, b) a = (a * b) % mod
#define repi(i,m,n) for(int i = m;i < n;i++)
#define drep(i,n,m) for(int i = n;i >= m;i--)
#define rep(i,n) repi(i,0,n)
#define rrep(i,n) repi(i,1,n+1)
#define chmin(x,y) x = min(x,y)
#define chmax(x,y) x = max(x,y)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(), v.rend()
#define dmp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
#define pf(x) push_front(x)
#define fi first
#define se second
// 許容する誤差ε
#define EPS (1e-10)
// 2つのスカラーが等しいかどうか
#define EQ(a,b) (abs((a)-(b)) < EPS)
// 2つのベクトルが等しいかどうか
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
//template
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p){
  os << "(" << p.first << "," << p.second << ")";return os;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v){
  for (auto it = v.begin();it != v.end();++it){
    if(it != v.begin())os << " ";os << *it;
      }return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &mp){
  for(auto x: mp)os << "(" << x.first << "," << x.second << ")" << endl;
  return os;
}
template<typename T, int SIZE>
int array_length(const T (&)[SIZE]){return SIZE;}
template<typename T, int N>
void PRINTF(const T (&a)[N], int s = N, int t = -1, bool f = true){
	if(t == -1){rep(i,s){if(i)cout << " ";cout << a[i];}}
	else repi(i,s,t){if(i!=s)cout << " ";cout << a[i];}
	if(f)cout << "\n";
}
template<typename T, int N1, int N2>
void PRINTF(const T (&a)[N1][N2], int h = N1, int w = N2){
	rep(i,h){rep(j,w){cout << a[i][j] << " \n"[j==w-1];}}
}
//typedef
typedef complex<double> Point;
typedef pair<int,int> P;
typedef pair<int, P> PP;
typedef pair<P, int> Pi;
typedef vector<int> vi;
typedef deque<int> dq;
const int inf = 1e9+7;
const int INF = 1e18+7;


double dot(Point a, Point b) {
  return (a.real() * b.real() + a.imag() * b.imag());
}
double cross(Point a, Point b) {
  return (a.real() * b.imag() - a.imag() * b.real());
}
bool cmp_x(const Point &p1, const Point &p2){
  if(p1.real() == p2.real())return p1.imag() < p2.imag();
  return p1.real() < p2.real();
}
class GrahamScan{
public:
  vector<Point> ps;
  int n;
  void init(int N){
    ps.clear();
    n = N;
  }
  void add_point(int x, int y){
    ps.push_back(Point(x, y));
  }
  vector<Point> graham_scan(){  //作った凸のvectorを返す
    sort(ps.begin(), ps.end(), cmp_x);
    int k = 0;
    vector<Point> qs(2*n);
    for(int i = 0;i < n;i++){   //下側凸の作成
      while(k > 1 && cross(qs[k-1]-qs[k-2], ps[i]-qs[k-1]) <= 0)k--;
      qs[k++] = ps[i];
    }
    for(int i = n-2, t = k;i >= 0;i--){   //上側凸の作成
      while(k > t && cross(qs[k-1]-qs[k-2], ps[i]-qs[k-1]) <= 0)k--;
      qs[k++] = ps[i];
    }
    qs.resize(k-1);
    return qs;
  }
};


signed 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]) != EOF){
    GrahamScan G;G.init(4);
    rep(i,4)G.add_point(X[i], Y[i]);
    vector<Point> vec = G.graham_scan();
    if(vec.size() == 4)printf("YES\n");
    else printf("NO\n");
  }
	return 0;
}











Measured memory_bytes: 3208