#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n; //树的高度

    int hour = 0;
    int finish = 0;
    //hour=1--->3
    //hour=2--->3-1

    //hour=3--->3-1+3

    while (finish < n) {
        hour++;
        if (hour % 2 > 0) finish += 3;
        else finish -= 1;
    }
    cout << hour << endl;

    return 0;
}