import java.util.Scanner;


public class Main
{   
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        int r , x1 , y1 , x2 , y2 , ans = 0;
        double dist , d;
        
        r = scan.nextInt();
        x1 = scan.nextInt();
        y1 = scan.nextInt();
        x2 = scan.nextInt();
        y2 = scan.nextInt();
        
        // 进行处理
        dist = getDist(x1 , y1 , x2 , y2);
        d = 2 * r;

        // 如果距离为0
        if (dist == 0)
            System.out.println(0);
        // 如果距离小于等于直径
        else if (dist <= d)
            System.out.println(1);
        // 如果距离大于直径
        else
        {
            while (dist > d)
            {
                dist -= d;
                ans ++;
            }
            // 如果有多余的距离
            if (dist < d)
                ans ++;
            System.out.println(ans);
        }
    }
    
    private static double getDist(int x1 , int y1 , int x2 , int y2)
    {
        return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    }
	
}








