#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<stack>
using namespace std;


int main()
{
   
  
    int n,z=0; cin >> n;
    

        while (n != 0)
        {
            if(n>=2)
               n -= 2;
            else if (n == 1)
                n -= 1;
            z++;

        }

        cout << z;
    
    return 0;
    
   
    
 }
