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
The missing number is 4.