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# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
namespace atcorderpractice
{
    class Mainclass
    {
        public static void Main(string[] args)
        {

            string[] input = Console.ReadLine().Split(' ');
            int n = int.Parse(input[0]);
            int a = int.Parse(input[1]);
            int b = int.Parse(input[2]);
            int temp = 1;
            int temp2 = 1;
            int sum = 0;

            for (int i = 1; i <= n; i++)
            {

               // Console.WriteLine(i);
                if (i != a)
                {
                    if (i != b)
                    {
                        
                        for (int sub = 0; sub < i+1; sub++)
                        {
                            //  Console.WriteLine("sub" + sub);

                            temp *= n - sub;
                            temp2 *= i - sub;
                        }
                        sum += temp / temp2;
                        sum = (sum % (1000000000 + 7));
                    }
                }
              //  Console.WriteLine("temp " + temp);
                //Console.WriteLine("temp2 " + temp2);
                temp = 1;
                temp2 = 1;
               // Console.WriteLine("sum" + sum);
            }


          //  Console.WriteLine(sum %( 1000000000 + 7));





        }
    }
}