填空题

设有以下函数过程：
Function fun(m As Integer) As Integer
Dim k As Integer, sum As Integer
sum = 0
For k = m To 1 Step -2
sum = sum + k
Next k
fun = sum
End Function
若在程序中用语句 s = fun(10) 调用此函数，则s的值为 ______ 。