#include <iostream>
#include <cmath>
using namespace std;

struct Point 
{
    double x, y;
    Point(double x=0, double y=0) : x(x), y(y) {}
    
	double distance (const Point &o) const 
	{
        return sqrt((x - o.x) * (x - o.x) + (y - o.y) * (y - o.y));
    }

    Point operator+(const Point &o) const 
	{
        return Point(x+o.x, y+o.y);
    }
 
    Point operator-(const Point &o) const 
	{
        return Point(x-o.x, y-o.y);
    }
 
    Point operator*(const double m) const 
	{
        return Point(x*m, y*m);
    }
 
    Point operator/(const double d) const 
	{
        return Point(x/d, y/d);
    }
 
    double cross(const Point &o) const 
	{
        return x * o.y - y * o.x;
    }
 
    double dot(const Point &o) const 
	{
        return x * o.x + y * o.y;
    }
 
    double atan() const 
	{
        return atan2(y, x);
    }

    double norm() const 
	{
        return dot(*this);
    }

	double area(const Point &a,const Point &b) const
	{
		double t = (a.x - x) * (b.y - y);
		double t2 = (a.y - y) * (b.x - x);
		double areas = abs(t-t2);
		return  areas/2;
	}
};

int main()
{
	Point p1,p2;
	cin >> p1.x >> p1.y >> p2.x >> p2.y;
	cout << fixed;
	cout.precision(6);
	cout << p1.distance(p2) << endl;

	return 0;
}

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

using namespace std;

int main(){

	double x1, x2, y1, y2;

	cin >> x1 >> y1 >> x2 >> y2;

	if (x1 == x2){
		cout << setprecision(12) << fabs(y1 - y2) << endl;
	}
	else if (y1 == y2){
		cout << setprecision(12) << fabs(x1 - x2) << endl;
	}
	else {
		cout << setprecision(12) << sqrt(pow(fabs(x1 - x2), 2) + pow(fabs(y1 - y2), 2)) << endl;
	}

	return 0;
}
