#include <stdio.h>
#include <math.h>
int main ( )
{
    double Xa,Ya,Xb,Yb,Q,AB;
    scanf("%lf %lf",&Xa,&Ya);
    scanf("%lf %lf",&Xb,&Yb);
    Q=(Xa-Xb)*(Xa-Xb)+(Ya-Yb)*(Ya-Yb);
    AB=sqrt(Q);
    printf("%.3ld",AB);
    return 0;
}