Here is the na´ve algorithm :
(1) Take the first two values : put the greatest in memory.
(2) Take the next value and the value in memory. If the next value is greater than the one in memory, replace the memory value with the next value, otherwise proceed.
(3) Repeat (2) until you reach the last value.
(4) The last value is the greatest integer in the set.
Takes a lot of time for big sets. The other algorithms run a lot faster and are not that complicated (take values by pairs, halving the number of values each step, take them by triplets, dividing the number of values by 3 at each step). Variations of this algorithm return the 2nd, 3rd, 4th greatest value in the same time.
If your piece of software does not support sequential execution of code, then it is not possible to write a single formula that gives the greatest value of a set. Why don't you download GCC and write a quick 5-line program using the algorithm described here (or the improved one) ? It's free, and can solve absolutely any problem because it is Turing-complete (unlike your maths software)