#include <stdio.h>
#include<math.h>
int main() {
int x1 = 0;
int y1 = 0;
int x2 = 0;
int y2 = 0;
float circumference;
scanf("%d %d",&x1,&y1);
scanf("%d %d",&x2,&y2);
float euclidean_distance =sqrt((x1 - x2)*(x1 - x2)+(y1 - y2)*(y1 - y2));
float manhattan_distance = abs(x1-x2)+abs(y1-y2);
if(euclidean_distance>=manhattan_distance){
circumference = euclidean_distance - manhattan_distance;
printf("%f",circumference);
}
else{
circumference = manhattan_distance -euclidean_distance;
printf("%f",circumference);
}
return 0;
}