KR

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


double distance_from_x_to_y(double u, double v, double w, double z)
{

	return sqrt(pow((abs(u - w)), 2) + pow((abs(v - z)), 2));

}
int main()
{
	double u, v, w, z;
	cin >> u >> v >> w >> z ;
	cout << endl;
	cout<< distance_from_x_to_y(u, v, w, z);





}