import java.util.ArrayList;
import java.util.Scanner;
public class Distance {
public static void main(String[] args) {
ArrayList<Double> x = new ArrayList<Double>();
ArrayList<Double> y = new ArrayList<Double>();
setInputs(x, y);
System.out.println(getDistance(x, y));
}
public static double getDistance(ArrayList<Double> x, ArrayList<Double> y){
double distanceX = getDistanceX(x.get(0), x.get(1));
double squareX = distanceX * distanceX;
double distanceY = getDistanceY(y.get(0), y.get(1));
double squareY = distanceY * distanceY;
return Math.sqrt(squareX + squareY);
}
private static double getDistanceX(double x1, double x2){
double distanceX = x1 - x2;
if(distanceX < 0){
distanceX = distanceX * (-1);
}
return distanceX;
}
private static double getDistanceY(double y1, double y2){
double distanceY = y1 - y2;
if(distanceY < 0){
distanceY = distanceY * (-1);
}
return distanceY;
}
private static void setInputs(ArrayList<Double> x, ArrayList<Double> y){
Scanner sc = new Scanner(System.in);
//P1の座標を入力から受け取る
x.add(sc.nextDouble());
y.add(sc.nextDouble());
//P2の座標を入力から受け取る
x.add(sc.nextDouble());
y.add(sc.nextDouble());
}
}