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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
typedef long long ll;

ll calc(ll a, ll b, ll p) {
    if (b == 0) {
        return 1;
    } else if (b % 2 == 0) {
        ll d = calc(a, b / 2, p);
        return (d * d) % p;
    } else {
        return (a * calc(a, b - 1, p)) % p;
    }
}

int main(void){
  int i,j;
  //  dic_t dic[200000];
  int ii[100];
  int ilen[100];
	int ia,ib,ic;
  long total =0;
  long ans =1;
  scanf("%d %d %d",&ia,&ib,&ic);
//  printf("%d %d %d\n",ia,ib,ic);
  for(i=1;i<=ia;i++){
	if (i == ib || i == ic){
      ;
    }
    else{

		total += calc((ll)ia,(ll)i,(ll)1000000007);
//  printf("i%d  total%ld\n",i,total);
    }
  }
  printf("%ld\n",total);
	return 0;

}