# No.512 魔法少女の追いかけっこ
x, y = [int(z) * 1000 for z in input().split()]
n = int(input())
a = [int(s) for s in input().split()]
can_goal = 'YES'

t_koba = [d / x for d in a]
t_master = [d / y for d in a]

for i in range(n - 1):
    if t_koba[i] > t_master[i + 1]:
        can_goal = 'NO'
        break

print(can_goal)