#include <iostream>
#include <cmath>
#include <cassert>

struct Point
{
    double x;
    double y;
};
double distance( Point p1, Point p2)
{
    double d;
    d = pow( pow( p1.x-p2.x, 2) + pow( p1.y - p2.y, 1/2), 2);
    return d;
}
struct Linia
{
    Point p1;
    Point p2;
};
void test_distance()
{
    {
        Point a {2, 4};
        Point b { 2, 3};
        assert ( distance( a, b)== 1);
    }
    {
        Point a { -1, 5};
        Point b { 2, 9};
        assert ( distance( a, b)==5);
    }
}
bool prostopadla( Linia l1, Linia l2)
{
    int a1, a2;
    a1 = (l1.p2.y-l1.p1.y)/(l1.p2.x-l1.p1.x);
    a2 = (l2.p2.y-l2.p1.y)/(l2.p2.x-l2.p1.x);
    if ( a1 == 0 || a2 == 0)
    {
        if( a1 == 0 && a2 != 0 && l2.p2.x == l2.p1.x)
        {
            return true;
        }
        if( a2 == 0 && a1 != 0 && l1.p2.x == l1.p1.x)
        {
            return true;
        }
        return false;
    }
    else
        {
        if (a1 * a2 == -1) {
            return true;
        }
        return false;
    }
}
void test_prostopadla()
{
    {
    Linia l1 { { 0, 1},  0, 4}};
    Linia l2 { { 3, 5}, { 3, -2};
    assert ( prostopadla ( l1, l2)==true);
}
int main()
{

    return 0;
}