#include <stdio.h>
int main(){
int n, count;
while(scanf("%d", &n), n){
count = 0;
while(n > 2){
count += n / 3;
n = n / 3 + n % 3;
}
if(n == 2) ++count;
printf("%d\n", count);
}
return 0;
}原文：http://blog.csdn.net/chang_mu/article/details/20731483