X,Y=map(int,input().split())
N=int(input())
A=list(map(int,input().split()))

for i in range(N-1):
    x=A[i]#/X
    k=x*Y

    #print(k)

    if A[i+1]*X<k:
        print("NO")
        exit()
    else:
        pass

print("YES")