#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    first = (k*(k-1))-1
    last = first+2*k
    return ((last+1)**2)//4 - ((first+1)**2)//4

if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)