I'm using the current formula but I am getting an error when I save:'The formula expression is invalid: Incorrect parameter type for function 'OR()'. Expected Boolean, received Text'

Where do I need to look to correct this in the formula? Whats the best way to find the root of the problem with a formula with multiple functions?

IF ( OR (ISPICKVAL ([Case].Flagged__c , "C")

,

   (AND (

ISPICKVAL([Case].Flagged__c , "O"),

[Case].Option__c = FALSE) ) , "High",""))

||

IF( OR (

AND (IF (ISPICKVAL ([Case].Flagged__c , "Me"), [Case].Option__c = FALSE),

AND (ISPICKVAL([Case].Flagged__c , "Others"),

   [Case].Option__c = TRUE) , "Medium","Low")

) )

I'm using the current formula but I am getting an error when I save:'The formula expression is invalid: Incorrect parameter type for function 'OR()'. Expected Boolean, received Text'

Where do I need to look to correct this in the formula? Whats the best way to find the root of the problem with a formula with multiple functions?

IF (
OR (ISPICKVAL ([Case].Flagged__c , "C")
,
(AND (
ISPICKVAL([Case].Flagged__c , "O"),
[Case].Option__c = FALSE) ) , "High",""))
||
IF(
OR (
AND (IF (ISPICKVAL ([Case].Flagged__c , "Me"), 
[Case].Option__c = FALSE),

AND (ISPICKVAL([Case].Flagged__c , "Others"), 
[Case].Option__c = TRUE) , "Medium","Low")
)
)