CF1437E Make It Increasing

You are given an array of $ n $ integers $ a_1 $ , $ a_2 $ , ..., $ a_n $ , and a set $ b $ of $ k $ distinct integers from $ 1 $ to $ n $ . In one operation, you may choose two integers $ i $ and $ x $ ( $ 1 \le i \le n $ , $ x $ can be any integer) and assign $ a_i := x $ . This operation can be done only if $ i $ does not belong to the set $ b $ . Calculate the minimum number of operations you should perform so the array $ a $ is increasing (that is, $ a_1 < a_2 < a_3 < \dots < a_n $ ), or report that it is impossible.

The first line contains two integers $ n $ and $ k $ ( $ 1 \le n \le 5 \cdot 10^5 $ , $ 0 \le k \le n $ ) — the size of the array $ a $ and the set $ b $ , respectively. The second line contains $ n $ integers $ a_1 $ , $ a_2 $ , ..., $ a_n $ ( $ 1 \le a_i \le 10^9 $ ). Then, if $ k \ne 0 $ , the third line follows, containing $ k $ integers $ b_1 $ , $ b_2 $ , ..., $ b_k $ ( $ 1 \le b_1 < b_2 < \dots < b_k \le n $ ). If $ k = 0 $ , this line is skipped.

If it is impossible to make the array $ a $ increasing using the given operations, print $ -1 $ . Otherwise, print one integer — the minimum number of operations you have to perform.