#include<bits/stdc++.h>using namespace std;struct UNU{ int x,y;};UNU sol;struct DOI{ int xx,yy;};DOI sol1;int main(){ int p,p1; double rez; cin>>sol.x>>sol.y>>sol1.xx>>sol1.yy; p=(sol1.xx-sol.x)*(sol1.xx-sol.x); p1=(sol1.yy-sol.y)*(sol1.yy-sol.y); rez=(double)sqrt(p+p1); cout<<fixed<<setprecision(3)<<rez<<"\n"; return 0;}