#include
#include
void main()
{
float x1,y1,x2,y2;
float fdist = 0;
scanf("%f%f%f%f",x1,y1,x2,y2);
fdist = sqrtf((x2 - x2) * (x2 - x1) + (y2 - y1) * (y2 - y1));
printf("%.2f",fdist);
}