int select_kth_largest(int k, int *S, int n)
{ /* return the kth largest element from the ordered set S of integers */
  /* n is the number of elements in S */
  /* Algorithm : if n < 50 then sort in dec. order S, return kth largest element
	                 in S
		 else
			divide S into ceil(n/5) sequences of 5 elements each 
			with upto four leftover elements
			sort in dec order each 5 element sequence
			let M be the sequence of medians of the 5 element sets
			m = select_kth_largest(ceil(n(M)/2), M, n/5);
			let S1, S2 and S3 be the sequences of elements in S 
			greater than, equal to and less than m respectively.
			if n(S1) >=k then return select_kth_largest(k, S1, n(S1));
			else
				if (n(S1) + n(S2) >= k) then return m
				else 
			return select_kth_largest (k - n(S1) - n(S2), S3);