#include<stdio.h>
#include<math.h>
int main ()
{
    int x1,x2,y1,y2,x,y,i;
    double z;
    x=abs(x2-x1)*abs(x2-x1);
    y=abs(y2-y1)*abs(y2-y1);
    z=sqrt(x+y);
    printf("%.8lf\n",z);
    return 0;
}



