import java.util.Scanner;

public class Main {

	public static void main(String args[]){

		Scanner cin = new Scanner(System.in);

		int X = cin.nextInt();
		int Y = cin.nextInt();
		int N = cin.nextInt();
		int A[] = new int[N];
		long sum = 0L;
		boolean result = true;
		double rate = (Y-X)/X;

		for(int i=1;i<=N;i++){
			A[i-1] = cin.nextInt();
			if(i>1){
				if(sum*rate>(double)A[i-1]){
					result = false;
					break;
				}
			}
			sum += (long)A[i-1];
		}
		
		if(result){
			System.out.println("YES");
		}else{
			System.out.println("NO");
		}

	}
}