#!/bin/python

import sys

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

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