https://www.cnblogs.com/--lr/p/6212936.html
#include <stdio.h>
#include <stdlib.h>
int main()
{
int x1,y1,x2,y2,x3,y3;
while(scanf("%d%d%d%d%d%d",&x1,&y1,&x2,&y2,&x3,&y3)!=EOF)
{
printf("3\n");
printf("%d %d\n",x1+x2-x3,y1+y2-y3);
printf("%d %d\n",x2+x3-x1,y2+y3-y1);
printf("%d %d\n",x1+x3-x2,y1+y3-y2);
}
return 0;
}