ss = input().split()
x = int(ss[0])
y = int(ss[1])
n = int(input())
a = list(map(int,input().split()))

hi = y / x
d = 0
for i in range(len(a) - 1):
    d += a[i]
    if d * hi - d > a[i + 1]:
        print("NO")
        break
else:
    print("YES")