import java.io.BufferedReader;
import java.io.FileReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.io.PrintWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.io.*;
import java.util.Random;
import java.text.DecimalFormat;
import java.lang.Math;
import static java.lang.Math.sqrt;
public class Main{
    public static void main(String[] args) {
            double k =1e6;
            double f =0;
            while(k-->0){
                Random g = new Random();
                double x1= g.nextDouble();
                double y1= g.nextDouble();
                double x2= g.nextDouble();
                double y2= g.nextDouble();
                f+=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
            }
              System.out.println(f/(1e6));
    }
}