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

	scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
	x = (x2 - x1) * (x2 - x1);
	y = (y2 - y1) * (y2 - y1);
	
	printf("%d\n", sqrt(x + y));
	
	return(0);
}
