【cf440A】Forgotten Episode

2014年6月4日9270

Polycarpus adores TV series. Right now he is ready to finish watching a season of a popular sitcom “Graph Theory”. In total, the season has n episodes, numbered with integers from 1 to n.

Polycarpus watches episodes not one by one but in a random order. He has already watched all the episodes except for one. Which episode has Polycaprus forgotten to watch?

Input

The first line of the input contains integer n (2 ≤ n ≤ 100000) — the number of episodes in a season. Assume that the episodes are numbered by integers from 1 to n.

The second line contains n - 1 integer a1, a2, …, an (1 ≤ ai ≤ n) — the numbers of episodes that Polycarpus has watched. All values ofai are distinct.

Output

Print the number of the episode that Polycarpus hasn’t watched.

Sample test(s)
input

output

题解

不解释