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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        D solver = new D();
        solver.solve(1, in, out);
        out.close();
    }

    static class D {
        static final long mod = 1000000007;

        public void solve(int testNumber, Scanner in, PrintWriter out) {

            long n = Long.parseLong(in.next());
            long a = Long.parseLong(in.next());
            long b = Long.parseLong(in.next());
            out.println((mod + mod + mod + powAndMod(2, n) - 1 - combinationAndMod(n, a) - combinationAndMod(n, b)) % mod);

        }

        static long combinationAndMod(long n, long r) {
            r = Math.min(r, n - r);
            long x = 1, y = 1;
            for (long i = 1; i <= r; i++) {
                x = x * (n - r + i) % mod;
                y = y * i % mod;
            }
            return x * powAndMod(y, mod - 2) % mod;
        }

        static long powAndMod(long a, long b) {
            long x = 1;
            while (b > 0) {
                if (b % 2 == 1) {
                    x = x * a % mod;
                    b--;
                } else {
                    a = a * a % mod;
                    b /= 2;
                }
            }
            return x;
        }

    }
}