using prompt output in a formula

Hi,
 
I have a report which displays data from 2 queries.
 
In query1 i am displaying the customer number from a table.
In Query2 retrieves the customer numbers  which is output of report prompt.
 
In  the report i am merging the customer numbers from Query1 and Query2.  and displaying it.

I need to display an additional column prompt_flag which shows whether the customer number is output of user prompt in query2.
 
eg:Query1 (From Table)
Cutomer Number
C1
C2
 
Query2 (From Prompt)
Cutomer Number
C3
C4
 
Report Output --
Cutomer Number             Prompt_flag
C1                                     0
C2                                     0
C3                                     1
C4                                     1
 
I have created the below formula to derive Prompt_flag.

=If(ToNumber(UserResponse([Query 2];"Enter values for Customer No:"))=[Customer No];1;0)

The above prompt works fine when i input only 1 customer_number.

But the problem now is that when i input multiple customer numbers in the prompt,the user response will display them as semicolon separated values.
 
ie, When i enter customer nos. C3 and C4 in the report prompt, user response displays them as C3;C4 which is of CHARACTER type .
Due to this , the function mentioned above is throwing error(#ERROR).
Any suggestions here ?
 
Regds,
HH