N, K = map(int, input().split())
MOD = 10 ** 9 + 7


def perm(n, k, mod=MOD):
    res = 1
    for i in range(k):
        res = res * (n - i) % mod
    return res


def seq_sum(n, mod=MOD):
    return (n * (n + 1) // 2) % mod


if K == 1:
    ans = seq_sum(N) * (N - 1)
else:
    ans = perm(N - 1, K) * seq_sum(N) + perm(N - 2, K - 2) * K * (K - 1) // 2 * seq_sum(N - 1)
ans %= MOD
print(ans)