#include <bits/stdc++.h>
using namespace std;
int main(){
    long long n;
    cin >> n;
    if(n < 3)cout << n << endl;
    else {long long ans = n + (n-2) + (n-4);
    long long te = (n-2)+(n-4);
    cout << ans + te << endl;
    }
}