#include <cmath>
#include <iostream>

int main() {
    double x1,y1,x2,y2,x3,y3,x4=0,y4=0;
    const double EPS=1e-9;
    std::cout << "Введите x1 y1 x2 y2 x3 y3: ";
    if (!(std::cin>>x1>>y1>>x2>>y2>>x3>>y3)) {
        std::cout << "Ошибка ввода.\n"; return 0;
    }
    bool found=false;
    double dot1=(x2-x1)*(x3-x1)+(y2-y1)*(y3-y1);
    double dot2=(x1-x2)*(x3-x2)+(y1-y2)*(y3-y2);
    double dot3=(x1-x3)*(x2-x3)+(y1-y3)*(y2-y3);
    if (std::fabs(dot1)<EPS) { x4=x2+x3-x1; y4=y2+y3-y1; found=true; }
    else if (std::fabs(dot2)<EPS) { x4=x1+x3-x2; y4=y1+y3-y2; found=true; }
    else if (std::fabs(dot3)<EPS) { x4=x1+x2-x3; y4=y1+y2-y3; found=true; }
    if (found) std::cout << "Четвёртая вершина: (" << x4 << "; " << y4 << ").\n";
    else std::cout << "Ошибка: точки не задают прямоугольник.\n";
    return 0;
}