MOD = 10 ** 9 + 7
N, M = map(int, input().split())
dp = [[0] * (N - M + 1) for _ in range(3)]
dp[0][0] = 1
for i in range(M + 1):
    dp[(i + 1) % 3] = [0] * (N - M + 1)
    for j in range(N - M + 1):
        if i > 0:
            dp[i % 3][j] += dp[(i - 1) % 3][j] * (M - i + 1)
        if j > 0:
            dp[i % 3][j] += dp[i % 3][j - 1] * i
        dp[i % 3][j] %= MOD
print(dp[M % 3][N - M])