Winter Supplies
Kopatych is a kind and hardworking bear-gardener who grows food for all the Smeshariki. During the winter, he usually hibernates, but he always ensures there are ample supplies for the other Smeshariki so they don't have to worry during the cold months.
As winter approaches, Kopatych begins preparing food supplies. He calculates the total amount of food he has and determines how many jars each type will fill. Interestingly, he finds that each type of food fills an even number of jars. As a result, after packing, he ends up with 2k jars of food.
Being meticulous, Kopatych decides to number all the jars. The winter, during which Kopatych sleeps, lasts for two months. To simplify things for the Smeshariki, he assigns negative numbers to the jars for the first month and positive numbers for the second month. He follows two additional rules: First, jars containing the same product must have numbers with the same absolute value. Second, the number of jars for each product must be equal for both months.
However, this morning, Kopatych discovered a problem: one of the jars had disappeared overnight. Now, he needs to figure out the number on the missing jar based on the numbers on the remaining jars.
Input
The first line of the input contains an odd integer n (1 ≤ n < 100000) - the number of jars that remain with Kopatych. The next line contains n integers a_i (1 ≤ |a_i| ≤ 1000) - the numbers on all the jars that remain.
Output
Output a single integer - the number that was on the jar that disappeared.