#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;


class Solution {
public:
    void rezolvare (string fileInput, string fileOutput){
        ifstream fileIn; fileIn.open(fileInput, ios::in);
        ofstream fileOut; fileOut.open(fileOutput, ios::out);

        // From here we start the problem.
        fileIn >> number;
        
        countFractii = number;
        countFractii += floor((double)number * number / 4);
        countFractii += ceil((double)number * 2 / 3) * floor((double)(number - 1) / 2);
        
        fileOut << countFractii;
        fileIn.close(); fileOut.close();
    }

private:
    long long int number{0};
    long long int countFractii = 0;
};

int main()
{
    Solution s;
    s.rezolvare("fractii.in", "fractii.out");
    return 0;
}