#!/bin/python3

import sys

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

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