/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(x(2, 3));
		System.out.println(x(100, 5));
		System.out.println(x(42, 0));
		System.out.println(x(0, 3));
		System.out.println(x(0, 0));
	}
 
	public static int x(int n, int p)
	{
		return -((p%2<1) ? p*p/2+p : p/2 * (p+2) + 1) + n - p*n;
	}
}

LyogcGFja2FnZSB3aGF0ZXZlcjsgLy8gZG9uJ3QgcGxhY2UgcGFja2FnZSBuYW1lISAqLwoKaW1wb3J0IGphdmEudXRpbC4qOwppbXBvcnQgamF2YS5sYW5nLio7CmltcG9ydCBqYXZhLmlvLio7CgovKiBOYW1lIG9mIHRoZSBjbGFzcyBoYXMgdG8gYmUgIk1haW4iIG9ubHkgaWYgdGhlIGNsYXNzIGlzIHB1YmxpYy4gKi8KY2xhc3MgSWRlb25lCnsKCXB1YmxpYyBzdGF0aWMgdm9pZCBtYWluIChTdHJpbmdbXSBhcmdzKSB0aHJvd3MgamF2YS5sYW5nLkV4Y2VwdGlvbgoJewoJCVN5c3RlbS5vdXQucHJpbnRsbih4KDIsIDMpKTsKCQlTeXN0ZW0ub3V0LnByaW50bG4oeCgxMDAsIDUpKTsKCQlTeXN0ZW0ub3V0LnByaW50bG4oeCg0MiwgMCkpOwoJCVN5c3RlbS5vdXQucHJpbnRsbih4KDAsIDMpKTsKCQlTeXN0ZW0ub3V0LnByaW50bG4oeCgwLCAwKSk7Cgl9CgkKCXB1YmxpYyBzdGF0aWMgaW50IHgoaW50IG4sIGludCBwKQoJewoJCXJldHVybiAtKChwJTI8MSkgPyBwKnAvMitwIDogcC8yICogKHArMikgKyAxKSArIG4gLSBwKm47Cgl9Cn0=