hdoj2001

 #include<iostream>
#include<cmath>
using namespace std;
int main()
{
    double x1,y1,x2,y2;
    cout.precision(2);
    while( cin >> x1 >> y1 >> x2 >> y2)
    {
           cout << fixed << sqrt(pow((x1-x2),2)+pow((y1-y2),2)) << endl;
           }
    system("pause");
    }