#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;cin>>n;
    int ans = 0;
     
    while(n!=0){
        if(n%3==0){
            ans += n/3;
            n = 0;
            break;
        }
        ans +=1;
        n = n-2;
    }
    cout<<ans<<endl;
    return 0;
}