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.io.PrintWriter;
import java.util.*;
import java.io.InputStream;
import java.io.DataInputStream;
 
 
public class Main
{ //static{ System.out.println(" hello ");}

   
  public static void main(String[] args) throws IOException
     { 
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastReader scn = new FastReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
     
        
        long k=scn.nl();
        long n=scn.nl();
        long w=scn.nl();
        long a=((w*(w+1))/2 ) * k;
        if (a<=n) out.println(0);
        else out.println(a-n);
        
        
        
        
           out.close();
     }
    
     
     
  
   }       
  class num //implements Comparator<num>
    {
        
        public int start;
        public int end;
        num()
        {
            
        }
        num(int x,int y)
        {
            this.start = x;
            this.end =y;
        }
        public int getstart()
        {
        return start;
        }
        public int getend()
        {
        return end;
        }
    /*    public boolean equals(Object n1)
        {num n=(num)n1;
        if (this.start==n.start && this.end==n.end) return true;
        else return false;
            
            
        }
        
        
         public int hashCode() 
         {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + start;
        result = prime * result+end;
               
        return result;
       }
       
       
        
       public int compare(num o1, num o2) {
              if (o1.getstart() > o2.getstart())
            return (o1.getstart()-o2.getstart());
            else if (o1.getstart() == o2.getstart())
            return (o1.getend()-o2.getend());
            else 
            return (o1.getstart()-o2.getstart());
            
        }
      */  
        
        
    }
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
class FastReader
{
 
    public InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;
 
    public FastReader(InputStream stream)
    {
        this.stream = stream;
    }
 
    public int read()
    {
        if (numChars == -1)
        {
            throw new InputMismatchException ();
        }
        if (curChar >= numChars)
        {
            curChar = 0;
            try
            {
                numChars = stream.read (buf);
            } catch (IOException e)
            {
                throw new InputMismatchException ();
            }
            if (numChars <= 0)
            {
                return -1;
            }
        }
        return buf[curChar++];
    }
    
 public char nc()
    {
        int c = read ();
        while (isSpaceChar (c))
            c = read ();
        return (char) c;
    }
    
    public int ni()
    {
        int c = read ();
        while (isSpaceChar (c))
            c = read ();
        int sgn = 1;
        if (c == '-')
        {
            sgn = -1;
            c = read ();
        }
        int res = 0;
        do
        {
            if (c < '0' || c > '9')
            {

                
            }
            res *= 10;
            res += c - '0';
            c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
    }
 
    public long nl()
    {
        int c = read ();
        while (isSpaceChar (c))
            c = read ();
        int sgn = 1;
        if (c == '-')
        {
            sgn = -1;
            c = read ();
        }
        long res = 0;
        do
        {
            if (c < '0' || c > '9')
            {
                throw new InputMismatchException ();
            }
            res *= 10;
            res += c - '0';
            c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
    }
 
    public String ns()
    {
        int c = read ();
        while (isSpaceChar (c))
            c = read ();
        StringBuilder res = new StringBuilder ();
        do
        {
            res.appendCodePoint (c);
            c = read ();
        } while (!isSpaceChar (c));
        return res.toString ();
    }
 
    public boolean isSpaceChar(int c)
    {
        if (filter != null)
        {
            return filter.isSpaceChar (c);
        }
        return isWhitespace (c);
    }
 
    public static boolean isWhitespace(int c)
    {
        return c==' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }
 
    public String next()
    {
        return ns ();
    }
 
    public interface SpaceCharFilter
    {
        public boolean isSpaceChar(int ch);
    }
}   