#include<stdio.h>
int main()
{
    double x1,y1,x2,y2,dis;

    scanf("%lf %lf",&x1,&y1);

    scanf("%lf %lf",&x2,&y2);

    dis=sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));

    printf("%.4lf\n",dis);

    return 0;
}