Average C++

Hello, I need help doing a c++ program. 

Here's the program i must do:

3 evaluators will evaluate 4 parameters ( just name them parameter1, parameter2 ...) the program must ask the evaluators to input those parameters but as letters (N=1,M=2,S=3,B=4,E=5) then I have to do the average for each evaluator and then the average for all of the 3 evaluators. 

Thank you, not sure if you guys understood my question.