#!/bin/python3

import sys
def sumoff(z):
    return (z*(z+1))//2
def sumOfGroup(k):
    s=sumoff(k-1)*2+1
    l=[]
    for i in range(s,s+(2*k),2):
        l.append(i)
    return sum(l)
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)