C :

#include<stdio.h>
int main()
{
	int n;
  while(~scanf("%d",&n))
  {
  	if(n==0)break;
    printf("%d\n",n/2);
  }
  return 0;
}

C++ :

#include<iostream>
using namespace std;
int main()
{
	int n,a;
while((cin>>n)&&n!=0)
	{   
		int s=0;	
	   while(n>=3)
        {
		a=n/3;
		s+=a;
	    n=a+n%3;   
		}
	    if(n%3==2)
			s++;
	cout<<s<<endl;
	}return 0;
}

Pascal :

  var
  n,s,a:integer;

  begin
   readln(n);

   while n<>0 do
    begin
     s:=0;
      while n>=3 do
       begin
        a:=n div 3;
        s:=s+a;
        n:=a+n mod 3;
       end;
       if n mod 3=2 then s:=s+1;
       writeln(s);
       readln(n);
    end;


  end.