小數點處理

#include <cstdlib>

#include <iostream>

#include <iomanip>

#include <cmath>

using namespace std;

int main(int argc, char *argv[])

{

    double x1,y1,x2,y2;

    while (cin>> x1>>y1>>x2>>y2)

    {

      double r = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));

      cout <<  fixed  <<  setprecision(3)<< r  << endl;

    }    

}