#include <bits/stdc++.h>
using namespace std;
#define int long long 
struct Point {
    int x, y;
};
int crossProduct(Point p1, Point p2, Point p3) {
    return (p2.x - p1.x) * (p3.y - p2.y) - (p2.y - p1.y) * (p3.x - p2.x);//判断是否逆时针 
}
bool isConvexPolygon(int n, const vector<Point>& vertices) {
	int cross[n];
    for (int i = 0; i < n; ++i) {
        cross[i] = crossProduct(vertices[i], vertices[(i + 1) % n], vertices[(i + 2) % n]);
    }
    int cnt=0;
    if(cross[0]==0){
    	cnt++;
	}
    for(int i=1;i<n;i++){
    	if(cross[i]*cross[i-1]<0){
    		return false;
		}
		if(cross[i]==0){
			cnt++;
		}
	}
	if(cnt==n){
		return false;
	}
	return true;
}
signed main() {
    int n;
    cin >> n;

    vector<Point> vertices(n);
    for (int i = 0; i < n; ++i) {
        cin >> vertices[i].x >> vertices[i].y;
    }
    bool result = isConvexPolygon(n, vertices);

    if (result) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }

    return 0;
}