4 人解决，7 人已尝试。
7 份提交通过，共有 34 份提交。
8.1 EMB 奖励。
单点时限: 2.0 sec
内存限制: 256 MB
TASK
Adam has a fancy for numbers. Once he found a batch of empty paper cards in his drawer, wrote random numbers on both sides of each card and thought of the following puzzle: what smallest possible value can be obtained by putting all cards in an arbitrary order (and upturned if necessary) to the expression of the following form:
_ - _ + _ - _ + _ - _ + … _
After a while Adam came up with a solution. Could you do that too? Write a program to solve the puzzle described above.
The first line contains the number of cards N (2 <= N <=10 0000, N is an even integer). Each of the following N lines contains two integers ai and bi (-2000 ≤ ai, bi ≤ 2000; i = 1…N). These are the numbers written on separate sides of the i-th card.
The first and the only line should contain the minimal value that can be obtained by putting all the cards to the expression as described above.
6 -8 12 0 5 7 -3 10 -7 -2 7 1 4
-34 Hint: Cards are put to the expression in this order: 1st, 2nd, 3rd, 5th, 4th, 6th. (-8) - 5 + (-3) - 7 + (-7) - 4 = -34
4 人解决，7 人已尝试。
7 份提交通过，共有 34 份提交。
8.1 EMB 奖励。