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.*;


public class CFSoldierAndBananas {


    public static void main(String[] args) {

        FastReader sc=new FastReader();
        int k=sc.nextInt();
        int n=sc.nextInt();
        int w=sc.nextInt();
        int d=n-(w*(w+1)/2*k);
        if(d<0)System.out.println(Math.abs(d));
        else System.out.println(0);
    }
    
}

class FastReader{
    BufferedReader br ;
    StringTokenizer st;
public FastReader(){
    InputStreamReader inr =new InputStreamReader(System.in);
    br=new BufferedReader(inr);

}

String next(){
    while(st==null || !st.hasMoreElements()){
    try{
    st=new StringTokenizer(br.readLine());
    }
    catch(IOException e){
        e.printStackTrace();
    }}
    return st.nextToken();
}

int nextInt(){
    return Integer.parseInt(next());
}

double nextDouble(){
    return Double.parseDouble(next());

}

long nextLong(){
    return Long.parseLong(next());
}


String nextLine(){
    String str="";
    try{
        str=br.readLine();
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }
    return str;
}
}
