#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
using namespace std;

int main() {
    int x, y,n; cin >> x >> y >> n;
    vector<int> a(n);
    rep(i,0,n) {
        cin>>a[i];
    }
    
    bool ok = 1;
    rep(i,0,n-1){
        ok &= a[i + 1] * x >= a[i] * y;
    }
    if (ok) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}