#include <iostream>
#include <vector>

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