백준 #10156번 과자

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		int k = sc.nextInt();
		int n = sc.nextInt();
		int m = sc.nextInt();
		
		if(k * n > m) {
			System.out.println(k * n - m);
		}else {
			System.out.println("0");
		}
		sc.close();
	}
}