#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start=1
    for i in range(2,k+1):
        start=start+2*(i-1)
    #print(start)
    return (k*start)+(k-1)*(k)

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