#include <iostream>
using namespace std;
int main(){
    bool chase=true;
    int X,Y,N,A[81]={0};
    cin >> X >> Y >> N;
    for(int i=1;i<=N;i++){
        cin >> A[i];
        if(X*A[i]<Y*A[i-1])chase=false;
    }
    cout << (chase?"YES":"NO") << endl;
    return 0;
}