import java.io.*;
import java.util.*;

public class Main {
  private Reader reader;
  private StreamTokenizer tokenizer;
  
  public Main() {
    reader = new BufferedReader(new InputStreamReader(System.in));
    tokenizer = new StreamTokenizer(reader);
  }
  
  public int nextInt() throws IOException {
    tokenizer.nextToken();
    
    return (int) tokenizer.nval;
  }
  
  public double nextDouble() throws IOException {
    tokenizer.nextToken();
    
    return tokenizer.nval;
  }
  
  public void exit() throws IOException {
    reader.close();
    
  }
  
  public static double distance(double x1, double y1, double x2, double y2) {
    return Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
  }
  
  public static void main(String[] args) throws IOException {
    Main main = new Main();
    
    double radius = main.nextDouble();
    double startX = main.nextDouble();
    double startY = main.nextDouble();
    double endX = main.nextDouble();
    double endY = main.nextDouble();
    
    System.out.println((int) Math.ceil(distance(startX, startY, endX, endY) / (2 * radius)));
    
    main.exit();
  }
}