//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int 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 = 0; i < N-1; i++){
    if(A[i]*Y <
      -A[i+1]*X){
      printl("NO");

      return 0;
    }
  }

  printl("YES");

  return 0;
}