x,y=map(int,input().split())
n=int(input())
A=list(map(int,input().split()))
memo=0
for i in range(n-1):
    Y=A[i+1]/y
    X=A[i]/x
    if X>Y:
        memo+=1
        break
if memo==0:
    print("YES")
else:
    print("NO")