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5605: Forgotten Episode

内存限制：256 MB 时间限制：2 S
题面：传统 评测方式：文本比较 上传者：
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题目描述

A. Forgotten Episode
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
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 of ai are distinct.
Output
Print the number of the episode that Polycarpus hasn't watched.
Examples
Input 
10
3 8 10 1 7 9 6 5 2
Output 
4

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