#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>

int main(void) {
	double x1, x2;
	double y1, y2;
	double distance = 0;
	double x = 0, y = 0;

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

	if (x1 < x2) {
		x = x2 - x1;
	}
	else if(x1 >= x2) {
		x = x1 - x2;
	}

	if (y1 < y2) {
		y = y2 - y1;
	}
	else if(y1 >= y2) {
		y = y1 - y2;
	}

	distance = (x*x) + (y*y);
	distance = sqrt(distance);

	printf("%f\n", distance);
	return 0;
}
