HOJ 2089 4th point

#include <stdio.h>

int main()
{
int i, j;
double x[5], y[5], x4, y4;

while (scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x[0], &y[0], &x[1], &y[1], &x[2], &y[2], &x[3], &y[3]) != EOF)
{
for (i = 0; i < 2; i++)
{
for (j = 2; j < 4; j++)
{
if ( (x[i] == x[j]) && (y[i] == y[j]) )
{
x[4] = x[i],y[4] = y[i];
break;
}
}
}
x4 = x[0] + x[1] + x[2] + x[3] - 3 * x[4];
y4 = y[0] + y[1] + y[2] + y[3] - 3 * y[4];
printf("%.3lf %.3lf\n", x4, y4);
}

return 0;
}