#!/bin/python3

import sys


def sumOfGroup(k):
    a = [i for i in range(1, pow(10,6), 2)]
    b = [int((i) * (i+1) / 2) for i in range(0, 1000)]
    c = [a[b[i]:b[i+1]] for i in range(0, 100)]
    return sum(c[k-1])
    
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)