#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;

#define ll         long long
#define PI         acos(-1.0)
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)

int main(){
    double X, Y;
    cin >> X >> Y;
    int N;
    cin >> N;
    double A[N];
    FOR(i,0,N) scanf("%lf",A+i);
    bool check = true;
    FOR(i,0,N-1){
        if(A[i]*Y>A[i+1]*X){
            cout << "NO" << endl;
            check = false;
            break;
        }
    }
    if(check) cout << "YES" << endl;
    return 0;
}