#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    j = 0
    for i in range(1,k):
        j += i
        
    odd = []
    for i in range(0,j*10):
        if i % 2 == 1:
            odd.append(i)
    
    res = 0
    for i in range(j, j+k):
        res += odd[i]
    
    return res
    
        
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)