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 solution{
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
 
        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        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 boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }
 
        public interface SpaceCharFilter {
 
            public boolean isSpaceChar(int ch);
        }
 
        public String next() {
            return nextString();
        }
        
        public char nextChar(){
        	int c=read();
        	while (isSpaceChar(c)) {
                c = read();
            }
        	return (char)c;
        }
 
        public String nextString() {
            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 int nextInt() {
            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') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public Long nextLong() {
            return Long.parseLong(nextString());
        }
 
        public Double nextDouble() {
            return Double.parseDouble(nextString());
        }
    }
    
    public static void main(String args[]){
        InputReader s=new InputReader(System.in);
        int k=s.nextInt();
        int n=s.nextInt();
        int w=s.nextInt();
        
        int price=k*(w*(w+1)/2);
        if(price>n)
            System.out.println(price-n);
        else
            System.out.println(0);
    }
    
}