help me do while function

Is the person a female or male? Enter F or M: x

It should be like this

Is the person a female or male? Enter F or M: f

The ideal weight is 145.94 pounds.

gender = input('Is the person a female or male? Enter F or M: ','s');

while (gender ~= F || gender ~= f || gender ~= M || gender ~= m)

gender = input('Is the person a female or male? Enter F or M: ','s');

end

what wrong with my code? Thanks

[Walter Roberson]

duplicates http://www.mathworks.co.uk/matlabcentral/answers/65065-help-me-do-while-function#answer_76621