Hatalı Kod Yardım

using System; 
  using System.Collections.Generic; 
  using System.ComponentModel; 
  using System.Data; 
  using System.Drawing; 
  using System.Linq; 
  using System.Text; 
  using System.Windows.Forms; 
   
  namespace Indirme_Sure_Hesaplama 
  { 
      public partial class Form1 : Form 
      { 
          public Form1() 
          { 
              InitializeComponent(); 
          } 
   
          private void timer1_Tick(object sender, EventArgs e) 
          { 
              
          } 
          private void button1_Click(object sender, EventArgs e) 
          { 
               try 
              { 
                  int boyut; int hiz; int kalansure; 
                  boyut = Convert.ToInt32(textBox1.Text); 
                  hiz = Convert.ToInt32(textBox2.Text); 
                   
                  if (comboBox1.SelectedText == "Kb" && comboBox2.SelectedText == "Kbps") 
                  { 
   
                      if (boyut%hiz*60 == 0) 
                      { 
                          kalansure = boyut / hiz*60; 
                          label4.Text = Convert.ToString(kalansure); 
                      } 
                      else 
                      { 
                          kalansure = boyut / hiz*60; 
                          label4.Text = Convert.ToString(kalansure) + " dakika" + Convert.ToString(boyut % hiz) + " saniye"; 
                      } 
   
   
                       
   
                  } 
                  else { label4.Text = ""; } 
   
              } 
              catch (Exception hata)  
              { 
                  if (hata.Message != "Input string was not in a correct format.") 
                  { 
                      MessageBox.Show(hata.Message); 
                  } 
              } 
               
               
              } 
          } 
      }