#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;


int main() {
	double x1, y1, z1, x, y, S;
	cin >> x >> y;
	cin >> x1 >> y1 >> z1;
	S = sqrt((x1-x)*(x1-x) + (y1-y)*(y1-y) + z1*z1);
	cout << fixed << setprecision(3) << 1/S;
	return 0;
}