n, a, b = map(int, input().split())

MOD = 10 ** 9 + 7


def comb(n, k):
    nCk = 1
    MOD = 10**9+7

    for i in range(n-k+1, n+1):
        nCk *= i
        nCk %= MOD

    for i in range(1, k+1):
        nCk *= pow(i, MOD-2, MOD)
        nCk %= MOD
    return nCk


print((pow(2, n, MOD) - 1 - comb(n, a) - comb(n, b) + MOD) % MOD)
