import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {
	static Scanner sc = new Scanner(System.in);
	static PrintWriter pw = new PrintWriter(System.out);

	public static void main(String[] args) throws IOException {
		// -------------------- Main ------------------
		int r = sc.nextInt(), x1 = sc.nextInt(), y1 = sc.nextInt(), x2 = sc.nextInt(),
				y2 = sc.nextInt();
		double d = Math.sqrt((x1-x2)*(x1-x2) +( y1-y2 )*(y1-y2)) ;
		pw.println((int)Math.ceil((d/2)/r));
		
		pw.flush();
		pw.close();
		// ---------------------------------------------
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public double nextDouble() throws IOException {
			return 0;
		}

		public boolean ready() throws IOException {
			return br.ready();
		}
	}

}
