import java.util.*;

public class Main{
        public static void main(String[] args){
                try(Scanner sc = new Scanner(System.in)){
                        long X = sc.nextLong(), Y = sc.nextLong();
                        int N = sc.nextInt();
                        long[] A = new long[N];
                        long Xlen = 0, Ylen = 0;
                        for(int i = 0; i < N; i++) {
                                A[i] = sc.nextLong();
                                Ylen = A[i];
                                if(i != 0) {
                                        Xlen = A[i-1];
                                        if(Xlen * Y > Ylen * X ) {
                                                System.out.println("NO");
                                                return;
                                        }
                                }
                        }
                        System.out.println("YES");
                }
        }
}