Buggy python submission (verdict: Runtime Error):
import sys
import math
from collections import deque

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()


def combinations_mod(n, r, mod=1000000007):
    """Returns nCr in mod."""
    r = min(r, n - r)
    combs = 1
    for i, j in zip(range(n - r + 1, n + 1), range(1, r + 1)):
        combs *= (i % mod) * pow(j, mod - 2, mod)
        combs %= mod
    return combs


def main():
    n, a, b = NMI()
    all = pow_mod(2, n, MOD) - 1
    ans = all - combinations_mod(n, a) - combinations_mod(n, b)
    ans %= MOD
    print(ans)



if __name__ == "__main__":
    main()

Fixed submission:
import sys
import math
from collections import deque

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()


def combinations_mod(n, r, mod=1000000007):
    """Returns nCr in mod."""
    r = min(r, n - r)
    combs = 1
    for i, j in zip(range(n - r + 1, n + 1), range(1, r + 1)):
        combs *= (i % mod) * pow(j, mod - 2, mod)
        combs %= mod
    return combs


def main():
    n, a, b = NMI()
    all = pow(2, n, MOD) - 1
    ans = all - combinations_mod(n, a) - combinations_mod(n, b)
    ans %= MOD
    print(ans)



if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import math
from collections import deque

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()


def make_grid(h, w, num): return [[int(num)] * w for _ in range(h)]


#隣接リスト 1-order
def make_adjlist_d(n, edges):
    res = [[] for _ in range(n + 1)]
    for edge in edges:
        res[edge[0]].append(edge[1])
        res[edge[1]].append(edge[0])
    return res


def make_adjlist_nond(n, edges):
    res = [[] for _ in range(n + 1)]
    for edge in edges:
        res[edge[0]].append(edge[1])
    return res


#nCr
def cmb(n, r):
    return math.factorial(n) // math.factorial(r) // math.factorial(n - r)


def cmb_mod(n, r, m):
    r = min(r, n-r)
    res = 1
    for i in range(0, r):
        res *= divide_mod(n-i, r-i, m)
        res %= m
    return res


def divide_mod(x, y, m):
    return (x%m) * pow_mod(y, m-2, m) % m


def pow_mod(base, exp, m):
    if exp == 1:
        return base % m
    elif exp % 2:
        return pow_mod(base, exp-1, m) * base % m
    else:
        return pow_mod(base, exp//2, m) ** 2 % m


def main():
    n, a, b = NMI()
    all = pow_mod(2, n, MOD) - 1
    ans = all - cmb_mod(n, a, MOD) - cmb_mod(n, b, MOD)
    ans %= MOD
    print(ans)



if __name__ == "__main__":
    main()

Fixed submission:
import sys
import math
from collections import deque

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()


def combinations_mod(n, r, mod=1000000007):
    """Returns nCr in mod."""
    r = min(r, n - r)
    combs = 1
    for i, j in zip(range(n - r + 1, n + 1), range(1, r + 1)):
        combs *= (i % mod) * pow(j, mod - 2, mod)
        combs %= mod
    return combs


def main():
    n, a, b = NMI()
    all = pow(2, n, MOD) - 1
    ans = all - combinations_mod(n, a) - combinations_mod(n, b)
    ans %= MOD
    print(ans)



if __name__ == "__main__":
    main()