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 C (GCC 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>
 long ncr(int n, int r){
      if (r==0 || n==r) {
        return 1;
    }
    else {
        return ncr(n-1, r) + ncr(n-1, r-1);
    }
}
int main(int argc, char const *argv[])
{
	long N,a,b,D=0;

	scanf("%ld %ld %ld",&N,&a,&b);
for (int i = 0; i < N; ++i)
{
D=D+ncr(N,i);
}

D=D-ncr(N,a);
D=D-ncr(N,b);


	printf("%ld\n",D%(1000000007) );
	return 0;
}