#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std ;
int main(){
    double d, x1,x2,y1,y2;
    cin>>x1>>y1;
    cin>>x2>>y2;
    if(x1<0||x1>50||x2<0||x2>50||y1<0||y1>50||y2<0||y2>50){
        cout<<"Invalid input";
        return 0;
    }
    else{
        d=(x2-x1)^2 +(y2-y1)^2;
        d =sqrt(d);
        cout<<fixed<<setprecision(2)<<d;
    }
}