Untitled

#include <iostream>
#include <math.h>
using namespace std;
double pisun(double x1, double y1, double x2, double y2) {
	double a = x2 - x1;
	double b = y2 - y1;
	double sum = sqrt(a * a + b * b);

	return sum;
}



int main()
{
	double x1,y1,x2,y2;
	cin >> x1 >> y1 >> x2 >> y2;
	double dist = pisun(x1, y1, x2, y2);
	cout << dist;
}