import sys

def solve():
    x, y = map(int, input().split())

    n = int(input())

    a = [int(i) for i in input().split()]

    x, y = 1, y/x

    for i, ai in enumerate(a[:-1]):
        if y * ai > a[i + 1]:
            print('NO')
            return

    print('YES')

if __name__ == '__main__':
    solve()