#include <iostream>
#include <cctype>
#include <cstring>
#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
	double x1,y1,x2,y2;
	scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2);
	printf("%4lf\n",sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)));
	return 0;
	
}
#include <iostream>
#include <math.h>

using namespace std;


class point{
public:
	double x, y;
	int set();
};

int point::set()
{
	cin >> x >> y;
	return 0;
}

int main()
{
	point P1, P2;
	P1.set();
	P2.set();

	cout << fixed << sqrt((P1.x - P2.x)*(P1.x - P2.x) + (P1.y - P2.y)*(P1.y - P2.y)) << endl;

	return 0;
}