#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>
#define DN 1000005

using namespace std;

int res[DN];

int main() {
    int n;
    //freopen("input.txt","r",stdin);
    cin >> n;
    res[1] = 1;
    res[2] = 3;
    for(int i = 3; i <= n; ++i){
        if(res[i-2] == 0)
            res[i] = res[i-2] + 1;
        else
            res[i] = res[i-2] - 1;
    }
    cout << 15 + res[n];
}