Trick was with I\O. I held half of contest myselt trying to pass it. If you use C\C++, you may have the same bug. Reading
scanf("%d%d\n",&n,&m); gets(a);
got WA#7, but this code
scanf("%d%d",&n,&m); gets(a); gets(a);
got AC. Why? I don't know! But it would be better to learn more about this bug. What do you think about it?

Safe Bird can you explain why his first code is wrong?

scanf("%d%d\n",&n,&m) reads not only new line character but leading spaces in second line.
If you use C++, you must know it!

Don't mix up 'scanf' and 'gets' or you will have unpredictable am-I-before-or-after-EOL situations. If you have to use 'gets' in the problem, use ONLY 'gets', and use 'sscanf' to extract row elements from the string fetched via 'gets', or use 'strtok' if you don't know amount of elements beforehand. For this particular problem I wrote:

gets(s);
sscanf(s, "%d %d", &n, &m);
gets(s);

>> scanf("%d%d\n",&n,&m) reads not only new line character  but leading spaces in second line.
>> If you use C++, you must know it!

Thank you for explain! :)

Edited by author 12.08.2008 22:09

2Igor E. Tuphanov
Thank you! You are very helpful!

Thank you for your useful tip!
I didn't find any document about this behavior. Your experience is really great.