Untitled

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

double null(int x1, int x2, int y1, int y2)
{
	double koren = double(sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2)));

	return double(koren);
}

int main() {
	float x1=0, y1=0, x2=0, y2=0;
	cin >> x1;
	cin >> y1;
	cin >> x2;
	cin >> y2;

	cout << null(x1, x2, y1, y2);

}