import java.util.*;
import java.lang.*;
import java.io.*;


class Main {
    public static int numberToSmoke(int n) {
        int sum=0;
        int cpt=0;
        for(int i=0; i<n; i++){
            cpt+=1;
            if(cpt==3){
                cpt=0;
                sum+=1;
                n+=1;
            }
        }
        return sum;
    }
    
    public static void main(String[] args) {
        System.out.println(numberToSmoke(1));//0
        System.out.println(numberToSmoke(6));//2
        System.out.println(numberToSmoke(12));//5
        System.out.println(numberToSmoke(101));//50
        System.out.println(numberToSmoke(198));//98
    }
}