There are n students in a university. The number of students is even. The i -th student has programming skill equal to a_i . The coach wants to form frac{n}{2} teams. Each team should consist of exactly two students, and each student should belong to exactly one team. Two students can form a team only if their skills are equal (otherwise they cannot understand each other and cannot form a team). Students can solve problems to increase their skill. One solved problem increases the skill by one. The coach wants to know the minimum total number of problems students should solve to form exactly frac{n}{2} teams (i.e. each pair of students should form a team). Your task is to find this number. The first line of the input contains one integer n ( 2 <= n <= 100 ) -- the number of students. It is guaranteed that n is even. The second line of the input contains n integers a_1, a_2, ... , a_n ( 1 <= a_i <= 100 ), where a_i is the skill of the i -th student. Print one number -- the minimum total number of problems students should solve to form exactly frac{n}{2} teams. In the first example the optimal teams will be: (3, 4) , (1, 6) and (2, 5) , where numbers in brackets are indices of students. Then, to form the first team the third student should solve 1 problem, to form the second team nobody needs to solve problems and to form the third team the second student should solve 4 problems so the answer is 1 + 4 = 5 . In the second example the first student should solve 99 problems to form a team with the second one.