import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    /*static long countArray(long ans ,int n, int k, int x) 
    {
        if(n == 1)
        {
            
        }
        else
        {
            ans = ans + countArray(ans , n-1, k, x);
        }
    }*/

    public static void main(String[] args) 
    {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();
        int x = in.nextInt();
        long ans = 0;
        n=n-1;
        
        while(n>0)
        {
            k--;
            ans = ans + k;
            n--;
        }
        
        //long answer = countArray(ans,n-1, k, x);
        ans = ans % (1000000007);
        System.out.println(ans);
        in.close();
    }
}