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] - a[i]: print("NO") break else: print("YES")