Presentation Error ??

[Md. Aftabuddin]

I received the following when I submitted a solution
Dear aftab:

Your C program has solved Ok the problem nnn (xxx xxx xxx xx)
in 0.000 seconds with low memory spent.
Congratulations!

Warning: Your program would get a Presentation Error in a true contest.
The 24-hours judge interpretes it as an "Accepted" problem.

What is ment by presentation Error ?
How to over come it ?

[misof]

Presentation error means: The data in your output is correct, but it is not formatted in the proper way. Check the problem statement. (Missing/excessive blank lines and unnecessary spaces are likely to have caused this message.)

[rahul007]

#include <stdio.h>

int main()

{
float s1,s2,y1,y2,y3;
int x1,x2,x3;

scanf("%d %d %d %d %d %d",&x1,&y1,&x2,&y2,&x3,&y3);

s1=(y2-y1)/(x2-x1);
s2=(y3-y2)/(x3-x2);

if(s1==s2)
{
printf("yes");
}
else
{
printf("no");
}
return 0;
}
I DON't understand what is the presentation error in this code??

[Zyaad Jaunnoo]

Rahul007, your solution is for what problem number on UVA Online Judge?