#include <iostream>
using namespace std;

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