X,Y = map(int,input().split())
N = int(input())
As = [int(x) for x in input().split()]
for i in range(N - 1):
    p = As[i]
    sight = As[i + 1]
    y_pos = int(p / X * Y)
    if y_pos > sight:
        print("NO")
        break
else:
    print("YES")