#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>

#include <functional>
#include <cassert>

typedef long long ll;
using namespace std;

#define debug(x) cerr << #x << " = " << (x) << endl;


#define mod 1000000007 //1e9+7(prime number)
#define INF 1000000000 //1e9
#define LLINF 2000000000000000000LL //2e18
#define SIZE 100010


int main(){
  
  int x,y,n;
  int a[100];

  cin >> x >> y >> n;

  for(int i=0;i<n;i++){
    scanf("%d",a+i);

    if(i > 0){
      if(a[i]*x < a[i-1]*y){
        puts("NO");
        return 0;
      }
    }
  }

  puts("YES");
  
  return 0;
}