#include <bits/stdc++.h>

using namespace std;

int main() {
    int x, y, n;
    cin >> x >> y >> n;

    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    
    for (int i = 0; i + 1 < n; ++i) {
        if (a[i] * y > a[i + 1] * x) {
            cout << "NO" << endl;
            return 0;
        }
    }
    
    cout << "YES" << endl;
    return 0;
}