Function QuandJour(a%, m%, j%, o%)
Dim x As Date
x = DateSerial(a, m - (o < 0), j) - (DateSerial(a, m - (o < 0), 6) Mod 7) + 7 * (o + IIf(o < 0, -(j <= DateSerial(a, m + 1, 6) Mod 7), j > DateSerial(a, m, 6) Mod 7))
If Month(x) = m Then QuandJour = x Else QuandJour = ""
End Function