#!/bin/python3

import sys

def oddPositive(num):
    l = list()
    l2 = list()
    j = 1
    for i in range(1, num):
        k = 0
        while(k != i):
            if (j % 2 != 0):
                l.append(j)
                k = k+1
            j = j+1
        l2.append(l)
        l = list()
    return l2

if __name__ == "__main__":
    k = int(input().strip())
    #answer = sumOfGroup(k)
    answer = oddPositive(k+1)
    sum = 0
    for x in answer[len(answer) - 1]:
        sum = sum + x
    print(sum)