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