#include <iostream>
#include <vector>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n); i++)

int main(){
    int x; cin >> x;
    int y; cin >> y;
    int n; cin >> n;
    vector<int>a(n);
    rep(i,n){
        cin >> a[i];
    }
    bool flag = true;
    rep(i,n-1){
        if(x * a[i + 1] < y * a[i])flag = false;
    }
    printf(flag ? "YES\n" : "NO\n");
    return 0;
}