Signal Panel Net Polarity

A diagnostic panel has a row of switches that a signal passes through, one after another, in order. Each switch is described by an integer reading: a positive reading passes the signal through unchanged, a negative reading inverts the signal's polarity, and a reading of exactly zero means that switch is broken -- it kills the signal completely, so nothing reaches the end of the panel regardless of any other switch.

Given the readings of every switch on the panel, determine the net polarity of the signal after it passes through all of them in order.

Input format

Line 1: an integer n -- the number of switches on the panel. Line 2: n space-separated integers a[0], a[1], ..., a[n-1] -- the reading of each switch, in the order the signal passes through them.

Output format

Print a single integer:

• 1 if the signal exits with positive net polarity (no broken switch, and an even number of inverting switches),
• -1 if the signal exits with negative net polarity (no broken switch, and an odd number of inverting switches),
• 0 if at least one switch is broken (reading exactly zero).

Constraints

• 1 <= n <= 1000
• -100 <= a[i] <= 100 for every i.

4
-3 5 -2 7

1

3
4 0 -9

0