Option Explicit
Sub Sommer()
Dim n As Long, Som As Currency, i As Long
Do While Not n >= 1
n = Int(Application.InputBox("Saisir un entier >= à 1 svp ?", Type:=1))
Loop
For i = 1 To n: Som = Som + i: Next i
MsgBox "La somme des entiers de 1 à " & Format(n, "#,##0") & " est : " & Format(Som, "#,##0")
End Sub