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Missing Number

Explanation

Here, we are provided n - 1 distinct numbers from 1 to n (inclusive).
Our task is to find the missing number from the sequence 1, 2, 3, ... n.

This can be done finding the sum of n numbers using (n * (n + 1)) / 2 and subtracting the sum of the given numbers from it.

Example

For numbers 1, 2, 3, 4, 5, if the missing number was 2. Using our method would be following these steps:

sum_total = 1 + 2 + 3 + 4 + 5 sum_given = 1 + 3 + 4 + 5 ans = sum_total - sum_given = 2

Code

n = int(input())
s = sum(list(map(int, input().split())))

print(int((n * (n + 1)) / 2 - s))