import java.util.*; public class Main { public static void main(String[] args){ Scanner sc=new Scanner(System.in); while(sc.hasNext()){ int n=sc.nextInt();//空汽水瓶数 int count=0;//能喝汽水瓶数 if(n>0){ while(n>1){ count+=n/3; n=n%3+n/3; if(n==2){ n++; } } System.out.println(count); } } sc.close(); } }