// Online C++ compiler to run C++ program online
#include <iostream>
#include "unordered_map"
#include "algorithm"
using namespace std;

int main() {
    ios :: sync_with_stdio(false);
    cin.tie(0);
    
    int tc = 1;
    //cin>>tc;
    while(tc--){
        int n;
        cin>>n;
        int cnt = n/3;
        cnt = cnt + (n%3)/2;
        cout<<cnt<<endl;
    }

    return 0;
}