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

public class CF507B {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		int r = Integer.parseInt(st.nextToken());
		int x = Integer.parseInt(st.nextToken());
		int y = Integer.parseInt(st.nextToken());
		int x_ = Integer.parseInt(st.nextToken());
		int y_ = Integer.parseInt(st.nextToken());
		System.out.println((int) Math.ceil(Math.hypot(x - x_, y - y_) / (2 * r)));
	}
}
