from decimal import Decimal as d
k, s = map(int, input().split())

n = int(input())

cr = list(map(int,input().split()))

for i in range(n-1):
    kd = cr[i]
    if d(kd/k * s) > cr[i+1]:
        print('NO')
        break
    else:
        continue
else:
    print('YES')