Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys

MOD = 1000000007  # type: int

class ModOperator:
    def __init__(self, MOD: int = 10 ** 9 + 7):
        self.MOD = MOD
        self.factorials = [1, 1]    # 階乗のメモ

    # x^n % MOD
    def mod_pow(self, x: int, n: int):
        bi = str(format(n, "b"))
        res = 1
        a = x
        for i in range(len(bi)):
            if n >> i & 1:
                res = (res * a) % self.MOD
            a = (a * a) % self.MOD
        return res
    
    # x! % MOD
    def mod_fact(self, x: int):
        if x < len(self.factorials):
            return self.factorials[x]
        else:
            res = self.factorials[-1]
            for i in range(len(self.factorials), x + 1):
                res = res * i % self.MOD
                self.factorials.append(res)
        return res % self.MOD

    # inverse of a number
    def mod_inv(self, x: int):
        return self.mod_pow(x, self.MOD - 2)
    
    # conmination nCk
    def mod_comb(self, n: int, k: int):
        numerator = self.mod_fact(n)
        denomintator1 = self.mod_fact(k)
        denomintator2 = self.mod_fact(n - k)
        denomintator = denomintator1 * denomintator2 % self.MOD
        return numerator * self.mod_inv(denomintator) % self.MOD


def main():
    n, a, b = map(int, input().split())
    op = ModOperator()
    print((op.mod_pow(2, n) - op.mod_comb(n, a) - op.mod_comb(n, b) - 1) % MOD)

    return


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys

MOD = 1000000007  # type: int

class ModOperator:
    def __init__(self, MOD: int = 10 ** 9 + 7):
        self.MOD = MOD

    def mod_pow(self, x: int, n: int):
        bi = str(format(n, "b"))
        res = 1
        a = x
        for i in range(len(bi)):
            if n >> i & 1:
                res = (res * a) % self.MOD
            a = (a * a) % self.MOD
        return res
    
    def mod_fact(self, x: int):
        res = 1
        for i in range(1, x + 1):
            res = res * i % self.MOD
        return res % self.MOD
    
    def mod_partial_fact(self, x: int, y: int):
        res = 1
        for i in range(x - y + 1, x + 1):
            res = res * i % self.MOD
        return res % self.MOD

    def mod_inv(self, x: int):
        return self.mod_pow(x, self.MOD - 2)
    
    def mod_comb(self, n: int, k: int):
        numerator = self.mod_partial_fact(n, k)
        denomintator = self.mod_fact(k)
        return numerator * self.mod_inv(denomintator) % self.MOD

def solve(n: int, a: int, b: int):
    op = ModOperator()
    print((op.mod_pow(2, n) - op.mod_comb(n, a) - op.mod_comb(n, b) - 1) % MOD)

    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    n = int(next(tokens))  # type: int
    a = int(next(tokens))  # type: int
    b = int(next(tokens))  # type: int
    solve(n, a, b)

if __name__ == '__main__':
    main()