C# - Binding TextBox to an integer

How to bind a TextBox to an integer? For example, binding unit to textBox1.

public partial class Form1 : Form
{
    int unit;

    public Form1()
    {
        InitializeComponent();


    }

    private void Form1_Load(object sender, EventArgs e)
    {
        textBox1.DataBindings.Add("Text", unit, "???");
    }