#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int X,Y; cin >> X >> Y;
    int N; cin >> N;
    vector<int> A(N);
    rep(i,N) cin >> A[i];
    int ok = 1;
    rep(i,N-1) {
        ok &= Y * A[i] <= X * A[i + 1];
    }
    cout << (ok ? "YES" : "NO") << endl;
}