#include<stdio.h>
#include<math.h>
int main(void)
{
	int a, b, c, d,e,x,y;
	double l;
	scanf("%d %d %d %d", &a, &b, &c, &d);
	if (a > c)
	{
		e = a;
		a = c;
		c = e;
	}
	if (b > d)
	{
		e = b;
		b = d;
		d = e;
	}
	x = (c - a)*(c - a);
	y = (d - b)*(d - b);
	l = x+y;
	printf("%f", sqrt(l));
	return 0;
}
