#!/usr/bin/env python3


def solve(x, y, n, zs):
    return all(zs[i] * y <= zs[i + 1] * x for i in range(n - 1))


def main():
    x, y = (int(p) for p in input().split())
    n = int(input())
    zs = [int(z) for z in input().split()]
    print("YES" if solve(x, y, n, zs) else "NO")


if __name__ == '__main__':
    main()