#include <iostream>
#include <stdio.h>
#include <iomanip>
#include <math.h>
using namespace std;
const int N = 1e6 + 10;
const int INF = 0x3f3f3f3f;
int main()
{
	float x1 , x2 , y1 , y2;
	cin >> x1 >> y1 >> x2 >> y2;
	x1 = ( x1 - x2 ) * ( x1 - x2 ) + ( y1 - y2 ) * ( y1 - y2 );
	x1 = sqrt( x1 );
	cout << fixed << setprecision(3) << x1;
}

/*******************************

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#include <stdio.h>
#include <iostream>
#include <math.h>
using namespace std;
int main()
{
	double x1, x2, y1, y2;
	cin >> x1 >> y1 >> x2 >> y2;
	double a, b;
	a = x1 - x2;
	b = y1 - y2;
	double c;
	c = a * a + b * b;
	c = sqrt(c);
	printf("%.3lf\n",c);
}

#include<stdio.h>
#include<iostream>
#include<math.h>
using namespace std;
int main()
{
    double a,b,c,d;
    cin >> a >> b >> c >> d;
    double a1,a2;
    a1 = fabs(c-a);
    a2 = fabs(d-b);
    double a3 = sqrt(a1*a1+a2*a2);
    printf("%.3lf",a3);
}

#include 
#include <iostream>
#include <math.h>
using namespace std;
int main(){
	double x1,x2,y1,y2;
	cin>>x1>>y1>>x2>>y2;
	double a,b;
	a=x1-x2;
	b=y1-y2;
	double c;
	c=a*a+b*b;
	c=sqrt(c);
	printf("%.3lf\n",c);
}

#include <iostream>
#include <math.h>
#include <iomanip>
using namespace std;
int main(){
    double x1,y1,x2,y2;
    cin>>x1>>y1>>x2>>y2;
    x1=((x1-x2)*(x1-x2))+((y1-y2)*(y1-y2));
    cout<<fixed<<setprecision(3)<<sqrt(x1)<<endl;
    return 0;
}

#include <stdio.h> #include <iostream> #include <math.h> using namespace std; int main() { double Xa , Xb , Ya ,Yb; cin >> Xa >> Xb ; cin >> Ya >> Yb; double x1 = Xa - Ya; double x2 = Xb - Yb; double x = (x1 * x1)+ (x2 * x2); printf("%.3lf\n",sqrt(x));

}

#include <stdio.h> #include <math.h> #include <iostream> using namespace std; int main() { double x1,x2,y1,y2; cin >> x1 >> y1 >> x2 >>y2; double a, b; a = x1 - x2; b = y1 - y2; double c; c = a * a + b * b; c = sqrt(c); printf("%.3lf\n",c); }

#include <math.h> #include <iostream> using namespace std; int main() { double x1, x2, y1, y2; cin >> x1 >> y1>> x2 >> y2; double a, b; a = x1 - x2; b = y1 - y2; double c; c =a * a + b * b; c =sqrt(c); printf("%.3lf\n",c); }

#include <stdio.h>
#include <math.h>
#include <iostream>
using namespace std;
int main()
{
	double x1,x2,y1,y2;
	cin >> x1 >> y1 >> x2 >>y2;
	double a, b;
	a = x1 - x2;
	b = y1 - y2;
	double c;
	c = a * a + b * b;
	c = sqrt(c);
	printf("%.3lf\n",c);
}

#include <stdio.h> #include <iostream> #include <math.h> #include <iomanip> using namespace std; int main() { double x1,x2,y1,y2; cin >> x1 >>y1 >> x2 >> y2; double a, b; a = x1 - x2; b = y1 - y2; double c; c = a * a + b * b; c = sqrt(c); printf("%.3lf\n",c); }