#include <bits/stdc++.h>
using namespace std;
double d1,d2,x,Min;
int main()
{
	Min=10000;
	x=3;
	while(x<15)
	{
		d1=sqrt(9+(x-3)*(x-3));
		d2=sqrt(36+(15-x)*(15-x));
		if(d1+d2<Min) Min=d1+d2;
		x=x+0.001;
	}
	printf("%10.2lf\n",Min);
	return 0;
}

NOIP2002