C# IF that checks wether a textbox input is greater than 0 and also checks if it's an integer(Numeric)

I made a scoreboard where the user inputs the max number of points allowed in a textBox1. I have two buttons. The left one increases the value on the left side of a label and the right one increases the value on the right side of the label. Once one side reaches the maximum number of points I declare the winner using a MessageBox.

I want to know how to check if the user didn't input an integer in the textbox. I already made te condition for it to be greater than 0.

This is what I have: SCOREBOARD IMAGE

 public void winner()
    {
        int max = Convert.ToInt32(textBox1.Text);

        if (max <= 0 || //this is where i want to check if its an integer)
        {
            MessageBox.Show("Press RESET and use a value greater than 0");
            btn_left.Enabled = false;
            btn_right.Enabled = false;
            textBox1.ResetText();
        }
        else if (left == max)
        {
            MessageBox.Show("Winner: Left Player");
            textBox1.Enabled = false;
            btn_left.Enabled = false;
            btn_right.Enabled = false;
        }
        else if (right == max)
        {
            MessageBox.Show("Winner: Right Player");
            textBox1.Enabled = false;
            btn_left.Enabled = false;
            btn_right.Enabled = false;
        }
    }
   private void btn_left_Click(object sender, EventArgs e)
    {
        left = left + 1;
        lbl_score.Text = left.ToString() + " - " + right.ToString();
        winner();
    }

    private void btn_right_Click(object sender, EventArgs e)
    {
        right = right + 1;
        lbl_score.Text = left.ToString() + " - " + right.ToString();
        winner();
    }

    private void btn_reset_Click(object sender, EventArgs e)
    {
        textBox1.Enabled = true;
        textBox1.Text = "0";
        btn_left.Enabled = true;
        btn_left.Enabled = true;
        left = 0;
        right = 0;
        lbl_score.Text = left.ToString() + " - " + right.ToString();
    }