CF1687D Cute number

Ran is especially skilled in computation and mathematics. It is said that she can do unimaginable calculation work in an instant. —Perfect Memento in Strict Sense Ran Yakumo is a cute girl who loves creating cute Maths problems. Let $ f(x) $ be the minimal [square number](https://en.wikipedia.org/wiki/Square_number) strictly greater than $ x $ , and $ g(x) $ be the maximal square number not strictly less than $ x $ . For example, $ f(1)=f(2)=g(4)=g(8)=4 $ . "not strictly less than" means less than or equal to. A positive integer $ x $ is cute if $ x-g(x)

The first line contains one integer $ n $ ( $ 1 \leq n \leq 10^6 $ ) — the length of $ a $ . The second line contains $ n $ intergers $ a_1,a_2,\ldots,a_n $ ( $ 1 \leq a_1 \leq a_2 \leq \ldots \leq a_n \leq 2\cdot 10^6 $ ) — the array $ a $ .

Print a single interger $ k $ — the answer.

Test case 1: $ 3 $ is not cute integer, so $ k\ne 0 $ . $ 2,4,9,11 $ are cute integers, so $ k=1 $ .