Need Help with a Formula Field

Hi,

I am trying to create a formula field 'Total__c' which has a return type of number. The formula will calculate the sum total value of seven other fields (subject1 marks, subject2 marks ... etc) which are of text type. However, if a student is absent for subject4, the value entered in subject4 field will be 'Absent' and this should be treated as zero while calculating the Total__c. I have written the below formula, but an error pops up saying the character length is too high. Any help is appreciated.

IF(!ISNUMBER(English__c),0,Value(English__c))+IF(!ISNUMBER(Physics__c),0,Value(Physics__c))+ IF(!ISNUMBER(Maths__c),0,Value(Maths__c))+IF(!ISNUMBER(Chemistry__c),0,Value(Chemistry__c))+
IF(!ISNUMBER(Social__c),0,Value(Social__c))+IF(!ISNUMBER(Biology__c),0,Value(Biology__c))+
IF(!ISNUMBER(Economics__c),0,Value(Economics__c))

Thank you,
Satya