speed=map(int, raw_input().split())
n=int(raw_input())
A=map(int, raw_input().split())

sA=speed[0]
sB=speed[1]


for a in range(n-1):
    if float(A[a+1])/sB < float(A[a])/sA:
        print 'NO'
        break

else:
    print 'YES'