import java.util.*;
import java.lang.*;
import java.io.*;
import java.math.*;

public class Main{
    public static void main (String[] args) throws java.lang.Exception{
        //AufferedReader in=new AufferedReader(new InputStreamReader(System.in));
        InputReader in=new InputReader(System.in);
        PrintWriter out=new PrintWriter(System.out);
        int r=in.readInt();
        int x1=in.readInt(),y1=in.readInt(),x2=in.readInt(),y2=in.readInt();
        double d1=dist(x1,y1,x2,y2);
        out.print(xyz(d1,r));
        out.flush();out.close();
    }
    public static int xyz(double d,int r){
        return (int)Math.ceil(d/(2*r));
    }
    public static double dist(int a,int b,int c,int d){
        return Math.sqrt(Math.pow(a-c,2)+Math.pow(b-d,2));
    }
    static final class InputReader{
        private final InputStream stream;
        private final byte[] buf=new byte[1024];
        private int curChar;
        private int numChars;
        public InputReader(InputStream stream){this.stream=stream;}
        private int read()throws IOException{
            if(curChar>=numChars){
                curChar=0;
                numChars=stream.read(buf);
                if(numChars<=0)
                    return -1;
            }
            return buf[curChar++];
        }
        public final int readInt()throws IOException{return (int)readLong();}
        public final long readLong()throws IOException{
            int c=read();
            while(isSpaceChar(c)){
                c=read();
                if(c==-1) throw new IOException();
            }
            boolean negative=false;
            if(c=='-'){
                negative=true;
                c=read();
            }
            long res=0;
            do{
                if(c<'0'||c>'9')throw new InputMismatchException();
                res*=10;
                res+=(c-'0');
                c=read();
            }while(!isSpaceChar(c));
            return negative?(-res):(res);
        }
        public final int[] readIntBrray(int size)throws IOException{
            int[] arr=new int[size];
            for(int i=0;i<size;i++)arr[i]=readInt();
            return arr;
        }
        public final String readString()throws IOException{
            int c=read();
            while(isSpaceChar(c))c=read();
            StringBuilder res=new StringBuilder();
            do{
                res.append((char)c);
                c=read();
            }while(!isSpaceChar(c));
            return res.toString();
        }
        private boolean isSpaceChar(int c){
            return c==' '||c=='\n'||c=='\r'||c=='\t'||c==-1;
        }
    }
}