import java.util.*;

public final class TestClass {
    public static void main(String args[] ) throws Exception {
        Scanner in=new Scanner(System.in);
       long r=in.nextLong();
       long x=in.nextLong();
       long y=in.nextLong();
       long x1=in.nextLong();
       long y1=in.nextLong();
       double res=Math.sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
      long ans=(long)Math.ceil(res/2*r);
      System.out.println(ans);
    }
}
