#include <stdio.h>
#include <math.h>
int main()
{
    float x1,y1,x2,y2,d;
    scanf("%f %f",&x1,&y1);
    scanf("%f %f",&x2,&y2);
    d = sqrt(((x2-x1)*(x2-x1)) + ((y2-y1)*(y2-y1)) );
    printf("%.4f\n",d);

return 0;
}