#include<iostream>
#include<algorithm>
#include<cmath>
#include<stdio.h>
#include<cstdio>
using namespace std;

int main()
{
	double  x1, x2, y1, y2;
	cin >> x1 >> y1 >> x2 >> y2;
	double X = max(x1, x2) - min(x1, x2);
	double Y = max(y1, y2) - min(y1, y2);

	printf("%.8lf\n", sqrt(X*X + Y*Y));


	return 0;

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

int main() {
	double x1, y1, x2, y2;
	cin >> setprecision(10) >> x1;
	cin >> setprecision(10) >> y1; 
	cin >> setprecision(10) >> x2;
	cin >> setprecision(10) >> y2;
	cout << setprecision(10) << sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)) << endl;
	return 0;
}