#include <iostream>
#include <vector>
using namespace std;
int main(int argc, char* argv[])
{
	int X,Y;
	int N,i;
	cin>>X>>Y;
	cin>>N;
	vector<int> A(N);
	for (i=0;i<N;i++){
		cin>>A[i];
	}
	for (i=0;i<N-1;i++){
		double DS=(double)(A[i]*Y)/X;
		if (DS>A[i+1]){
			cout<<"NO"<<endl;
			return 0;
		}
	}
	cout<<"YES"<<endl;
	return 0;
}