Euler Problem 1

Euler Problem 1 ask;

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.

My Solution;

Sub Euler1()
   Dim a, b, c
   Dim SumA, SumB, SumC
   Dim Count, I  
   a = 3
   b = 5
   c = 15  
   Count = 999  
   For I = a To Count Step a
      SumA = SumA + I
   Next  
   For I = b To Count Step b
      SumB = SumB + I
   Next  
   For I = c To Count Step c
      SumC = SumC + I
   Next  
   MsgBox (SumA + SumB - SumC)
End Sub