#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>

using namespace std;

double EPS = 1e-10;

double add(double a, double b) {
	if (abs(a + b) < EPS * (abs(a) + abs(b))) {
		return 0;
	}
	return a + b;
}

struct P {
	double x, y;
	P() {}
	P(double x, double y) : x(x), y(y) {
	}
	P operator + (P p) {
		return P(add(x, p.x), add(y, p.y));
	}
	P operator - (P p) {
		return P(add(x, -p.x), add(y, -p.y));
	}
	P operator * (double d) {
		return P(x * d, y * d);
	}
	double dot(P p) {
		return add(x * p.x, y * p.y);
	}
	double det(P p) {
		return add(x * p.y , -y * p.x);
	}
};

bool cmp_x(const P& p, const P& q) {
	if (p.x != q.x) {
		return p.x < q.x;
	}
	return p.y < q.y;
}

vector<P> convex_hull(P* ps, int n) {
	sort(ps, ps + n, cmp_x);
	int k = 0;
	vector<P> qs(n*2);

	for (int i = 0; i < n; i++) {
		while (k > 1 && (qs[k-1] - qs[k-2]).det(ps[i] - qs[k-1]) <= 0) {
			k--;
		}
		qs[k++] = ps[i];
	}
	for (int i = n-2, t = k; i >= 0; i--) {
		while (k > t && (qs[k-1] - qs[k-2]).det(ps[i] - qs[k-1]) <= 0) {
			k--;
		}
		qs[k++] = ps[i];
	}
	qs.resize(k-1);
	return qs;
}

P ps[10];

int main() {
	char c;
	while (cin >> ps[0].x >> c >> ps[0].y >> c >> ps[1].x >> c >> ps[1].y >> c >> ps[2].x >> c >> ps[2].y >> c >> ps[3].x >> c >> ps[3].y) {
		vector<P> qs = convex_hull(ps, 4);
		if (qs.size() == 4) {
			cout << "YES" << endl;
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}