hdu2001 c++

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


int main()
{
double a1, a2, b1, b2;
while(cin>>a1>>a2>>b1>>b2)
{
double dis;
dis= sqrt(pow(b1-a1,2)+pow(b2-a2,2));
cout<<fixed<<setprecision(2)<<dis<<endl;
}

return 0;
}