#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = int((k-1)*((k-1)+1)/2)*2 + 1
    sum1 = int((k-1)*((k-1)+1)/2)*2
    sum2 = k*start
    
    return sum1 + sum2

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