A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k dollars for the second one and so on (in other words, he has to pay i·k dollars for the i-th banana). 

He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?

Input

The first line contains three positive integers k, n, w (1 ≤ k, w ≤ 1000, 0 ≤ n ≤ 109), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants. 

Output

Output one integer — the amount of dollars that the soldier must borrow from his friend. If he doesn't have to borrow money, output 0.

Examples

Input

3 17 4


Output

13
import java.io.*;
import java.util.HashMap;


public class Main{
  public static void main(String[] args) throws Exception {
    try{
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      String str[] = br.readLine().split(" ");
      int k = Integer.parseInt(str[0]);
      int n = Integer.parseInt(str[1]);
      int w = Integer.parseInt(str[2]);

      int sum=0;
      for(int i=1;i<=w;i++){
        sum+=i*k;
      }

      sum = sum - n;

      if(sum <= 0){
        System.out.println("0");
      }else{
        System.out.println(Math.abs(sum));
      }
      
    }catch(Exception e){
      return;
    }
  }
}
