using namespace std;
	int a,b,c,d,x,y;
int main(){
	cin>>a>>b>>c>>d;
	x=abs(a-c);
	y=abs(d-b);
	cout<<fixed<<setprecision(2)<<sqrt(x*x+y*y) << endl;


	
	return 0;
}

组合拳奥！（两点距离公式有但我就不用(￣ε(#￣)☆╰╮o(￣皿￣///)）

#include<bits/stdc++.h> using namespace std; int main() { double a,b,c,d,x; cin>>a>>b>>c>>d; x= (a-c)(a-c)+(b-d)(b-d); x=fabs(x); x=sqrt(x) ; printf("%.2lf",x); return 0 ; }

#include<bits/stdc++.h>
using namespace std;
	
int main(){
	double x1,y1,x2,y2;
	cin>>x1>>y1>>x2>>y2;
	printf("%.2lf",sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)));
	return 0;
}