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

double	cal_distance(double x1,double y1,double x2,double y2)
{

		double X,Y;
		double D,d;

		X = x2 - x1;
		Y = y1 - y2;

		D = (X*X)+(Y*Y);

		d = sqrt(D);
		
		return (d);
}

int main(void)
{

	int  x1, x2, y1, y2;
		double distance;
	
	scanf("%d %d %d %d",&x1, &y1, &x2, &y2);
	
	distance = cal_distance( x1,x2, y1,y2);
	
	printf("%d",distance);

	return 0;

}