import java.util.Scanner;

public class Convex_poligon {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int arrx[] = new int[n + 2];
        int arry[] = new int[n + 2];
        for (int i = 0; i < n; i++) {
            arrx[i] = sc.nextInt();
            arry[i] = sc.nextInt();
        }
        arrx[n] = arrx[0];
        arry[n] = arry[0];
        arrx[n + 1] = arrx[1];
        arry[n + 1] = arry[1];
        int s;
        int ch = -1;
        for (int i = 0; i < n; i++) {
            s = arrx[i] * arry[i + 1] - arrx[i + 1] * arry[i] + arrx[i + 1] * arry[i + 2] - arrx[i + 2] * arry[i + 1]
                    + arrx[i + 2] * arry[i] - arrx[i] * arry[i + 2];
            if (ch == -1) {
                if (s > 0)
                    ch = 1;
                if (s < 0)
                    ch = 0;
            } else {
                if (s < 0 && ch == 1) {
                    ch = 2;
                    break;
                }
                if (s > 0 && ch == 0) {
                    ch = 2;
                    break;
                }
            }
        }
        if (ch != 2)
            System.out.println("YES");
        else
            System.out.println("NO");
        sc.close();
    }
}