this function should return a complete numeric value lower then the max number in range and the highist possible value MISSING from the range

for exemple:
if the numbers in the range are 1, 9, 4 and 8 the result shold be 7
7 is lower then 9 (9 is the max value in range), a hole number (i dont want to see fractions) and as high as it gets and still not be one of the numbers in the range

i do not have programing/macro abilities in my excel (atlist non that i know of)
and i need to show the 3 highist number not chosen yet (i will use it 3 time and every time add the result to the range for the next one)

i can artificially add a max value to the range in order to limit it as i like, or the function can get a max value in separate