import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        double r = nextDouble();
        double x = nextDouble();
        double y = nextDouble();
        double x2 = nextDouble();
        double y2 = nextDouble();

        double d = Math.sqrt(Math.abs(x - x2) * Math.abs(x - x2) + Math.abs(y - y2) * Math.abs(y - y2));

        writer.println((int)Math.ceil(d / r / 2.0));

        writer.close();
    }

    static PrintWriter writer = new PrintWriter(System.out);

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer tokenizer = new StringTokenizer("");

    static String next() {
        while (!tokenizer.hasMoreTokens())
            try {
                tokenizer = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                return null;
            }
        return tokenizer.nextToken();
    }

    static int nextInt() {
        return Integer.parseInt(next());
    }

    static long nextLong() {
        return Long.parseLong(next());
    }

    static double nextDouble() {
        return Double.parseDouble(next());
    }
}