Conditional Date formula in Crystal Report

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C#

C#4.0

If I write this formula then an error arises. The error is like this
"The) is missing" how can I solve this please help me. I an new in crystal Report formula.
My formula is :

if {Table1.FDate}=""
then
{Table1.ToDate}=month({Table1.ToDate} date)
else
{Table1.FDate}