#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <algorithm>
#include <cassert>
#include <cmath>
#include <utility>
#include <map>
#include <set>
#include <vector>
#include <conio.h>

using namespace std;

double x11, y11, xc, yc, x2, y2, h, dh, a, t;

double f(double x)
{
    return 2 * (a - x) * (x*dh / a + h);
}

int main()
{

    scanf("%lf%lf%lf%lf%lf%lf", &xc, &yc, &x11, &y11, &x2, &y2);
    if (y2 >= yc)
    {
        printf("0");
        return 0;
    }

    if (x11 > x2)
    {
        x11 = t;
        x11 = x2;
        x2 = t;
    }

    if (y11 < y2)
    {
        y11 = t;
        y11 = y2;
        y2 = t;
    }

    a = xc - x11;
    h = y11;
    dh = yc - y11;

    if (dh - h > 0)
        printf("%lf", f(a*(dh - h) / (dh*2.0)));
    else
        printf("%lf", f(0));

    _getch();
    return 0;
}