OJ Board

Here is my code for 494 Kindergarten Counting Game.I'd seen all the posts about the problem 494, but still I got WA after the judge.
Will The judge system give a test single 'a'? If so, how can I output? My answer is '1'.
So everyone who can tell me the key point, Thanx ! :D
#include <stdio.h ...

Greetings!

The following operation is performed as long as there are at least two cards in the deck:
Throw away the top card and move the card that is now on the top of the deck to the bottom of the deck.

Your task is to find the sequence of discarded cards and the last, remaining card.

I ...

I'm ACM fresh and now I'm confused in the following code.I don't know where it has mistakes.So many times did I submit.Who can help me? :-?
#include <stdio.h>
#include <string.h>
int main()
{
char str[100], buf[10];
int i, j, len, flag, n;
scanf("%d%*c", &n);
while (n--)
{
gets(buf);
scanf ...