#include<iostream>
#include<iomanip>
#include<cmath>

int a1,b1,a2,b2;
double func(double x);

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;

    cin >> a1 >> b1 >> a2 >> b2;
    double delta = 1e-4;
    double head = 1e-4;
    double tail = 1000000+head;
    while(1)
    {
        double mid = 0.5*(head + tail);
        double cur = func(mid);
        double up = func(mid+delta);
        double down = func(mid - delta);
        if((cur-up)*(cur-down)>=0)
        {
            cout.setf(std::ios::fixed|std::ios::showpoint);
            cout.precision(9);
            cout << cur << endl;
            return 0;
        }else
        {
            if(up>=cur)
            {
                head = mid + delta;
            }
            else
            {
                tail = mid - delta;
            }
        }
    }

}
double func(double x)
{
    return sqrt((a1+b1*x)*(a1+b1*x)/(1 + x*x) + (a2+b2*x)*(a2+b2*x) / (1 + x*x));
}

try lond double for func & x, and long long for a1,a2,b1,b2.
i don't sure, but it must help...