Giới thiệu: Đây là đề thi ICPC

N + 1 (N is odd number) shoes from (N + 1)/2 pair of shoes the same type with different sizes are lined up in a random order. Aquarius, Taitruong, Loc, David secretly take one of the shoes out and hide it. Salmon need to guess whether the hidden shoe is for left foot or right foot and what is its size. Write a program to solve this game with cheating computer power.

Input

The first line of input contains the one integer N (1 ≤ N ≤ 100000), the number of shoes. The following line contains N integers S1, S2, ..., SN (1 ≤ |Si| ≤ 1000 000 000). Shoe i is for left foot if Si < 0, otherwise it is for right foot. The size of the shoe is |Si|.

Output

Output one integer R where |R| is equal to the hidden shoe is size and it is negative if it is a shoe for left foot, positive otherwise.

Examples

Input

3
1 2 -1

Output

-2