Deos aoynne uadrtesnnd waht am I tlaknig?

Consider this sentence

$\text{This sentence should not have any grammatical errors.}$

According to an investigation, humans still can interpret the sentence correctly, even though the letters of the word are lightly or well scrambled, but the first and the last letter are in the correctly placed and the arrangement of the words are correct.

As an example, the phrase, Fthaer and Mhtoer , will be interpreted as Father and Mother , since the arrangement of the words are correct and the first and the last letter are correct, even though it is well scrambled.

By satisfying the condition above, we will have $a^b+c^d+e^f+g^h$ "sentences" which we can read it fluently. What is $a+b+c+d+e+f+g+h$ ?

Details and Assumptions

The sentence given should be in your count since it satisfies the two condition above.

Do not bother about the phrase, the phrase is just to give you a concept on the main idea of the problem.