How to handle a FormatException if the user inputs letters?

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 Project2

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

private void convertTempButton_Click(object sender, EventArgs e)

{

int Fahrenheit;

int Celsius;

try

{

Fahrenheit = int.Parse(temperatureTextBox.Text);

}

catch (Exception ex)

{

MessageBox.Show("Please enter a Numeric Value");

}

Fahrenheit = int.Parse(temperatureTextBox.Text);

Celsius = (Fahrenheit - 32) * 5 / 9;

convertTempLabel.Text = Convert.ToString(Celsius) + " Celsius";

}