#include <stdio.h>
#include <math.h>
int main()
{
int x1, y1, x2, y2;
int x, y;
scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
x = abs(x1 - x2);
y = abs(y1 - y2);
float distance = sqrt((x*x) + (y * y));
printf("%.2f", distance);
return 0;
}