#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <iomanip>
#include <map>
using namespace std;
typedef long long LL;

int main(){
    LL n; 
    cin >> n;
    LL ans = 0;
    for(LL i = 1; i <= n; i++){
        ans = max(ans, (n-i)*(i+1)+i);
    }
    cout << ans << endl;
    return 0;
}