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

#include <math.h>

#include "point.h"



double distance(struct point p1, struct point p2) {
    // TODO: implement this function
    return 0;
}


int main(void) {
    struct point p1, p2;
    if (scanf("%d %d %d %d", &p1.x, &p1.y, &p2.x, &p2.y) != 4) { return 0; }
    printf("%g\n", distance(p1, p2));
    return 0;
}