using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp8
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int a = 0;

        private void button1_Click(object sender, EventArgs e)
        {
            a++;
            for (int i = 0; i < a; i++)
            {
                label1.Text += a.ToString();
                if (a % 3 == 0)
                    label1.Text += "0";
            }
        }
    }
}