#include<iostream>usingnamespace std;unsignedintsln(unsignedint N){if(N ==2|| N ==3){return1;}if(N <=1){return0;}unsignedint Total =0;while(N >3){
N -=2;
Total++;if(N ==2|| N ==3){
Total++;
N =0;}if(N ==2|| N ==3){
Total++;
N =1;}}return Total;}intmain(){unsignedint N;while(cin >> N){
cout <<sln(N)<< endl;}return0;}