#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int x,y;
  cin>>x>>y;
  Int n;
  cin>>n;
  vector<Int> a(n);
  for(Int i=0;i<n;i++) cin>>a[i];

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