#include <iostream>
#include <algorithm>
#include <utility>
#include <numeric>

int main()
{
    long long int n = 0;
    std::cin >> n;
    
    long long int max = 0;
    
    for( int i = 1; i < n; ++i )
    {
        max = std::max((n-i+1)*i + (n-i), max);    
    }
    
    std::cout << max << std::endl;
    
}