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

public class u {
	
	BufferedReader br;
	
	void solve() {
		br = new BufferedReader(new InputStreamReader(System.in));
		int r=Integer.parseInt(ns());
		int x1=Integer.parseInt(ns());
		int y1=Integer.parseInt(ns());
		int x2=Integer.parseInt(ns());
		int y2=Integer.parseInt(ns());
	    double dis=Math.sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
	    dis=dis/2;
	    dis=dis/r;
	    dis=Math.ceil(dis);
	    System.out.println((int)dis);
		

		
		

	}
	
	StringTokenizer input;
	
	String ns() {
		if(input == null || !input.hasMoreTokens()) {
			try {
				input = new StringTokenizer(br.readLine());
			} catch(IOException e) {
				throw new InputMismatchException();
			}
		} return input.nextToken();
	}
	
	public static void main(String[] args) {
		new u().solve();
	}
}