#include <iostream>
using namespace std;
int main(){
	int N;
	float X,Y;
	cin>>X>>Y>>N;
	int Xlength,Ylength=0;
	int ans=0;
	for(int i=0;i!=N;i++){
		Xlength=Ylength;
		int j;
		cin>>Ylength;
		if(Xlength*Y>Ylength*X){
			ans++;
			break;
		}
	}
	if(ans==0){
		cout<<"YES"<<endl;
	}else{
		cout<<"NO"<<endl;
	}
	return 0;
}