The Easy problem

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Easy, Easy
Problem

This time Princu wanted some nuf so he went to Param's room. There he saw Param playing with first N natural numbers. To have some nuf he took one number from param and hid it. Param being a programmer finds it easy to write a program to check the number which Princu hid instead of using old school methods. Help Param find the number

INPUT

The first line contains an integer N denoting total number of numbers Param originally had.

The next N-1 lines contains the numbers, the numbers currently present with Param

OUTPUT

Print the number that was hidden by Princu.

CONSTRAINTS

1 <= N <= 10^6

Time Limit: 1
Memory Limit: 256
Source Limit:
Explanation

The missing number is 4.

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