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

int main(void) {
    ll X,Y,N,A;
    cin >> X >> Y >> N;
    vector<ll> dis(N+1);
    bool up = true;
    double time;
    dis[0] = 0;
    for (int i = 1; i <= N; i++) {
        cin >> A;
        dis[i] = A + dis[i-1];
        time = (double)dis[i] / (double)Y;
        if ((double)dis[i-1] > time * (double)X) up = false;
    }
    cout << (up ? "YES" : "NO") << endl;
    return 0;
}