#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    index = ((k-1)*k)//(2)
    index += 1
    su = 0
    for i in range(k):
        temp = (index-1)*2+1
        su += (index-1)*2+1
        index += 1
    return su

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