#include <bits/stdc++.h>
using namespace std;

int main(void) {
    int X,Y,N,A,B;
    cin >> X >> Y >> N >> A;
    bool up = true;
    for (int i=1; i<N; i++) {
        B = A;
        cin >> A;
        if (B*Y > A*X) up = false;
    }
    cout << (up ? "YES" : "NO") << endl;
    return 0;
}