#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    n=k-1
    s,c=0,0
    n=(n*(n+1))/2;
    f=2*int(n)
    while c!=k:
        if f%2 !=0:
            s=s+f
            c+=1
        f+=1 
    return s
        
        

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