#include<bits/stdc++.h>
#define MAX_N 100001
#define INF_INT 2147483647
#define INF_LL 9223372036854775807
#define REP(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;

bool isPrime(int n){
  if(n == 2)
    return true;
  if(n % 2 == 0)
    return false;
  int sqr = sqrt(n)+1;
  for(int i=3;i<=sqr;i++){
    if(n % i == 0)
      return false;
  }
  return true;
}

bool cmp(pair<int,string> a,pair<int,string> b){
  if(a == b)
    return true;
  else if(a.first < b.first)
    return true;
  else if(a.first > b.first)
    return false;
  else if(a.second > b.second)
    return true;
  else
    return false;
}
bool cmpf(pair<int,string> a,pair<int,string> b){
  return a.first > b.first;
}
bool cmps(pair<int,string> a,pair<int,string> b){
  return a.second < b.second;
}



int main()
{
  ll X,Y,N,A[100];
  cin >> X >> Y;
  cin >> N;
  REP(i,N)cin >> A[i];
  REP(i,N-1){
    if(Y*A[i] > X*A[i+1]){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
  
}