using System;
using System.Windows.Forms;

namespace Phibonachi_Old
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private int Calculate(int number)
        {
            if (number == 0) { return 0; }
            else if (number == 1) { return 1; }
            else return Calculate(number - 1) + Calculate(number - 2);
        }

        private void button1_Click(object sender, EventArgs e)
        {

            if (!int.TryParse(textBox1.Text, out var number))
            {
                MessageBox.Show("Это не число!");
                textBox1.Text = null;
                return;
            }
            else label3.Text = Convert.ToString(Calculate(Convert.ToInt32(textBox1.Text)));
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}