#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    l = 1 + (k-1)*k
    theSum = 0;
    for i in range(0,k):
        theSum = theSum + l;
        l = l+2;
    return theSum

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