#!/bin/python3

import sys
import math
def sumOfGroup(k):
    n=k*(k-1)+1;
    i=int(0);
    sum=int(0);
    for i in  range(0,k):
        sum+=n;
        n+=2;
    return sum;
    # Return the sum of the elements of the k'th group.

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