#include <stdio.h>
#include <math.h>
int main ()
{
	double a , b , c , d  , e , f , g;
	scanf("%lf%lf",&a,&b);
	scanf("%lf%lf",&c,&b);
	e = (c-a)*(c-a);
	f = (d-b)*(d-b);
	g = e+f;
	printf("%.3lf",sqrt(g));
	return 0 ;
}