#include<stdio.h>
#include<math.h>
double dist(double x1,double y1,double x2,double y2);
int main()
{
double result,x1,x2,y1,y2;
scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
result=dist(x1,y1,x2,y2);
printf("%.2f",result);
return 0;
}
double dist(double x1,double y1,double x2,double y2)
{
double sum,x,y;
x=fabs(x1-x2);
y=fabs(y1-y2);
sum=sqrt(x*x+y*y);
return sum;
}