#include<bits/stdc++.h>
#define endl '\n'
using namespace std;
int main() {
    int n, r, d; cin >> n;
    r = n%3;
    d = n/3;
    if(r == 1) cout << (d-1) + 2;
    else if(r == 0) cout << d << endl;
    else if(r == 2) cout << (d + 1) << endl;

    return 0;
}