import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

MOD = 10**9 + 7

N, K = map(int, read().split())

# (0,1) に居たコマを重ならないように右に K 回動かしたときの、到達地点の組
dp = np.zeros((K+2, K+2), np.int64)
dp[0,1] = 1
for _ in range(K):
    newdp = dp * (N - 2)
    newdp[1:] += dp[:-1]
    newdp[:,1:] += dp[:,:-1]
    dp = newdp
    dp %= MOD
    np.fill_diagonal(dp, 0)

dp = dp.sum(axis=1) % MOD

coef = np.zeros(N+2, np.int64)
dp = dp[:N+1]
for i, x in enumerate(dp):
    coef[0] += x
    coef[N+1-i] -= x
coef %= MOD
np.cumsum(coef, out=coef)
coef %= MOD

x = (coef[:N + 1] * np.arange(N + 1, dtype=np.int64) % MOD).sum() % MOD
print(x)