Ошибка с выводом ответа в listbox. Задача на одномерный массив

Public Class Form1
    Dim rnd As New Random()
    Dim mas(14) As Int32
    Dim sum As Int32 = 0
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ListBox1.Items.Clear()
        For i As Int32 = 0 To mas.Length - 1
            mas(i) = rnd.Next(-45, 50)
 
            ListBox1.Items.Add("mas(" + i.ToString() + ") = " + mas(i).ToString())
 
        Next
    End Sub
 
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        ListBox2.Items.Clear()
        For i As Int32 = 0 To mas.Length - 1
            If mas(i) > 0 Then
                sum += mas(i)
            ElseIf mas(i) < 0 Then
                ListBox2.Items.Add("summa = " + sum.ToString())
            End If
        Next
    End Sub
End Class

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        ListBox2.Items.Clear()
        For i As Int32 = 0 To mas.Length - 1
            If mas(i) > 0 Then
                sum += mas(i)
                ListBox2.Items.Add("summa = " + sum.ToString())
            ElseIf mas(i) < 0 Then
                Exit Sub
 
            End If
 
        Next
    End Sub
End Class

 ListBox2.Items.Clear()
        For i As Int32 = 0 To mas.Length - 1
            If mas(i) > 0 Then
                sum += mas(i)
            ElseIf mas(i) < 0 Then
                ListBox2.Items.Add("summa = " + sum.ToString())
                Exit Sub
            End If
        Next