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.IOException;
import java.io.InputStream;
import java.util.InputMismatchException;

public class M{

	void solve()
	{
		int n = ni();
		int m = ni();
		int w = ni();
		int ans = (n*w*(w+1))/2;
		System.out.println(Math.max(ans-m,0));
	}
	
	public static void main(String[] args){new M().solve();}
	
	private byte[] bufferArray = new byte[1024];
	private int bufLength = 0;
	private int bufCurrent = 0;
	InputStream inputStream = System.in;
	
	int nextByte()
	{
		if(bufLength==-1)
			throw new InputMismatchException();
		if(bufCurrent>=bufLength)
		{
			bufCurrent = 0;
			try
			{bufLength = inputStream.read(bufferArray);}
			catch(IOException e)
			{ throw new InputMismatchException();}
			if(bufLength<=0)
				return -1;
		}
		return bufferArray[bufCurrent++];
	}
	
	boolean isSpaceChar(int x)
	{return (x<33 || x>126);}
	
	boolean isDigit(int x)
	{return (x>='0' && x<='9');}
	
	int nextNonSpace()
	{
		int x;
		while((x=nextByte())!=-1 && isSpaceChar(x));
		return x;
	}
	
	int ni()
	{
		int ans = 0;
		int sign = 1;
		int x = nextNonSpace();
		if(x=='-') 
		{
			sign = -1;
			x = nextByte();
		}
		while(!isSpaceChar(x))
		{
			if(isDigit(x))
			{
				ans = ans*10 + x -'0';
				x = nextByte();
			}
			else
				throw new InputMismatchException();
		}
		return sign*ans;
	}
	
	long nl()
	{
		long ans = 0;
		long sign = 1;
		int x = nextNonSpace();
		if(x=='-') 
		{
			sign = -1;
			x = nextByte();
		}
		while(!isSpaceChar(x))
		{
			if(isDigit(x))
			{
				ans = ans*10 + x -'0';
				x = nextByte();
			}
			else
				throw new InputMismatchException();
		}
		return sign*ans;
	}
	
	String ns()
	{
		StringBuilder sb = new StringBuilder();
		int x = nextNonSpace();
		while(!isSpaceChar(x))
		{
			sb.append((char)x);
			x = nextByte();
		}
		return sb.toString();
	}
	
	String nL()
	{
		StringBuilder sb = new StringBuilder();
		int x = nextNonSpace();
		while(x==32 || !isSpaceChar(x))
		{
			sb.append((char)x);
			x = nextByte();
		}
		return sb.toString();
	}
	
	char nc()
	{ return (char)nextNonSpace();}
	
	double nd()
	{ return (double)Double.parseDouble(ns()); }
	
	char[] ca()
	{ return ns().toCharArray();}
	
	char[] ca(int n)
	{
		char[] ans = new char[n];
		int p =0;
		int x = nextNonSpace();
		while(p<n)
		{
			ans[p++] = (char)x;
			x = nextByte();
		}
		return ans;
	}
	
	int[] ia(int n)
	{
		int[] ans = new int[n];
		for(int i=0;i<n;i++)
			ans[i]=ni();
		return ans;
	}
	
}
