Problem:
Score : 400 points

Problem Statement

Akari has n kinds of flowers, one of each kind.

She is going to choose one or more of these flowers to make a bouquet.

However, she hates two numbers a and b, so the number of flowers in the bouquet cannot be a or b.

How many different bouquets are there that Akari can make?

Find the count modulo (10^9 + 7).

Here, two bouquets are considered different when there is a flower that is used in one of the bouquets but not in the other bouquet.

Constraints

All values in input are integers.

2 \leq n \leq 10^9

1 \leq a < b \leq \textrm{min}(n, 2 \times 10^5)

Input

Input is given from Standard Input in the following format:

n a b

Output

Print the number of bouquets that Akari can make, modulo (10^9 + 7). (If there are no such bouquets, print 0.)

Sample Input 1

4 1 3

Sample Output 1

7

In this case, Akari can choose 2 or 4 flowers to make the bouquet.

There are 6 ways to choose 2 out of the 4 flowers, and 1 way to choose 4, so there are a total of 7 different bouquets that Akari can make.

Sample Input 2

1000000000 141421 173205

Sample Output 2

34076506

Print the count modulo (10^9 + 7).

Solution in Python (3.4.3) (judge verdict: Runtime Error)

n,a,b = map(int,input().split())
m = 10**9+7

def nCr(n_, r_, m_):
  c = min(r_ , n_ - r_)
  bunshi = 1
  bunbo = 1
  for i in range(1,c+1):
    bunshi = bunchi * (n_+1-i) % m_
    bunbo = bunbo * i % m_
  return bunshi * pow(bunbo, m_-2, m_) % m_


ans = pow(2,n,m)-1
ans -= nCr(n,a,m)
ans %= m
ans -= nCr(n,b,m)
ans %= m
print(ans)