1015

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main (){
    int x1, x2, y1, y2;



    scanf ("%d %d", &x1, &y1);
    scanf ("%d %d", &x2, &y2);


    printf ("%.4f\n", sqrt((pow((x2-x1), 2))+(pow((y2-y1), 2))));


    return 0;
}