Buggy python submission (verdict: Time Limit Exceeded):
import sys

sys.setrecursionlimit(10 ** 6)
INF = float("inf")
MOD = 10 ** 9 + 7


def input():
    return sys.stdin.readline().strip()


class ModInt:
    def __init__(self, x):
        self.x = x % MOD

    def __str__(self):
        return str(self.x)

    __repr__ = __str__

    def __add__(self, other):
        return (
            ModInt(self.x + other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x + other)
        )

    def __sub__(self, other):
        return (
            ModInt(self.x - other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x - other)
        )

    def __mul__(self, other):
        return (
            ModInt(self.x * other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x * other)
        )

    def __truediv__(self, other):
        return (
            ModInt(self.x * pow(other.x, MOD - 2, MOD))
            if isinstance(other, ModInt)
            else ModInt(self.x * pow(other, MOD - 2, MOD))
        )

    def __pow__(self, other):
        return (
            ModInt(pow(self.x, other.x, MOD))
            if isinstance(other, ModInt)
            else ModInt(pow(self.x, other, MOD))
        )

    __radd__ = __add__

    def __rsub__(self, other):
        return (
            ModInt(other.x - self.x)
            if isinstance(other, ModInt)
            else ModInt(other - self.x)
        )

    __rmul__ = __mul__

    def __rtruediv__(self, other):
        return (
            ModInt(other.x * pow(self.x, MOD - 2, MOD))
            if isinstance(other, ModInt)
            else ModInt(other * pow(self.x, MOD - 2, MOD))
        )

    def __rpow__(self, other):
        return (
            ModInt(pow(other.x, self.x, MOD))
            if isinstance(other, ModInt)
            else ModInt(pow(other, self.x, MOD))
        )


def main():
    N, A, B = map(int, input().split())
    total = ModInt(2) ** N - 1

    num_a = ModInt(1)
    for i in range(A):
        num_a *= N - i
        num_a /= A - i

    num_b = ModInt(1)
    for i in range(B):
        num_b *= N - i
        num_b /= B - i

    total -= num_a
    total -= num_b
    print(total)


if __name__ == "__main__":
    main()


Fixed submission:
import sys

sys.setrecursionlimit(10 ** 6)
INF = float("inf")
MOD = 10 ** 9 + 7


def input():
    return sys.stdin.readline().strip()


class ModInt:
    def __init__(self, x):
        self.x = x % MOD

    def __str__(self):
        return str(self.x)

    __repr__ = __str__

    def __add__(self, other):
        return (
            ModInt(self.x + other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x + other)
        )

    def __sub__(self, other):
        return (
            ModInt(self.x - other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x - other)
        )

    def __mul__(self, other):
        return (
            ModInt(self.x * other.x)
            if isinstance(other, ModInt)
            else ModInt(self.x * other)
        )

    def __truediv__(self, other):
        return (
            ModInt(self.x * pow(other.x, MOD - 2, MOD))
            if isinstance(other, ModInt)
            else ModInt(self.x * pow(other, MOD - 2, MOD))
        )

    def __pow__(self, other):
        return (
            ModInt(pow(self.x, other.x, MOD))
            if isinstance(other, ModInt)
            else ModInt(pow(self.x, other, MOD))
        )

    __radd__ = __add__

    def __rsub__(self, other):
        return (
            ModInt(other.x - self.x)
            if isinstance(other, ModInt)
            else ModInt(other - self.x)
        )

    __rmul__ = __mul__

    def __rtruediv__(self, other):
        return (
            ModInt(other.x * pow(self.x, MOD - 2, MOD))
            if isinstance(other, ModInt)
            else ModInt(other * pow(self.x, MOD - 2, MOD))
        )

    def __rpow__(self, other):
        return (
            ModInt(pow(other.x, self.x, MOD))
            if isinstance(other, ModInt)
            else ModInt(pow(other, self.x, MOD))
        )


def main():
    N, A, B = map(int, input().split())
    total = ModInt(2) ** N - 1
    MAX = max(A, B)
    MIN = min(A, B)

    num = ModInt(1)
    for i in range(MAX):
        if i == MIN:
            total -= num
        num *= N - i
        num /= i + 1

    total -= num
    print(total)


if __name__ == "__main__":
    main()