#include <bits/stdc++.h>
using namespace std;

int main(){
  int x,y;
  cin>>x>>y;
  int n;
  cin>>n;
  int a[n];
  for(int i=0;i<n;i++) cin>>a[i];
  for(int i=0;i<n-1;i++){
    if(a[i]*y<=a[i+1]*x) continue;
    else{
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;
  return 0;
}