#include<iostream>
using namespace std;

int main () {
    int X, Y;
    cin >> X >> Y;
    int N;
    cin >> N;
    int A[81];
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }
    for (int i = 0; i < N - 1; i++) {
        if (A[i] * Y > A[i + 1] * X) {
            cout << "NO" << endl;
            goto label;
        }
    }
    cout << "YES" << endl;
label:
    return 0;
}