#!/bin/python3

import sys
def sumOfGroup(k):
    l=(k*(k-1))/2
    l=int(l+1)
    p=l*2-1
    s=0
    for i in range(0,k):
        s=s+p
        p=p+2
    print(s)
    # Return the sum of the elements of the k'th group.

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