Convert seconds to HH:MM

Hi

I have a field i am getting from the database 'Seconds' as an int.

How in my crystal formula can i convert the int to the format HH:MM ?

It seems simple but this is not working....

Dim hr As Number 'to hold hrs part
Dim mn As Number 'to hold minutes
Dim sc As Number 'to hold seconds
Dim r1 As Number 'to hold reminders
Dim r2 As Number 'to hold reminders
Dim str As String 'to hold string hrs
Dim str1 As String 'to hold string minutes
Dim str2 As String 'to hold string seconds
Dim start as number

start = int({Summary.intInCourse}/{Summary.intUserTotal})
hr=start/ 3600 'get hours
r1=Remainder (start,3600 ) 'rest of seconds after hours taken out
mn=int(r1 / 60) 'get minutes
r2=Remainder (r1,60 ) 'rest of the seconds

'Convert all values in to strings to format in to "00" and to remove decimals
str=CStr (hr)
str1=CStr (mn)
str2=CStr (r2)

'to get rid off the decimal values
str = left(str, len(str)-3)
str1 = left(str1, len(str1)-3)
str2 = left(str2, len(str2)-3)

'format in to "00"
if len(str)<=1 then
str="0" & str
else
str= str
end if
if len(str1)<=1 then
str1="0" & str1
else
str1= str1
end if
if len(str2)<=1 then
str2="0" & str2
else
str2 = str2
end if
'Finally add to formula
formula= str & ":" & str1 & ":" & str2

any ideas??