OJ Board

#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 ...