CF1400E Clear the Multiset

You have a multiset containing several integers. Initially, it contains $ a_1 $ elements equal to $ 1 $ , $ a_2 $ elements equal to $ 2 $ , ..., $ a_n $ elements equal to $ n $ . You may apply two types of operations: - choose two integers $ l $ and $ r $ ( $ l \le r $ ), then remove one occurrence of $ l $ , one occurrence of $ l + 1 $ , ..., one occurrence of $ r $ from the multiset. This operation can be applied only if each number from $ l $ to $ r $ occurs at least once in the multiset; - choose two integers $ i $ and $ x $ ( $ x \ge 1 $ ), then remove $ x $ occurrences of $ i $ from the multiset. This operation can be applied only if the multiset contains at least $ x $ occurrences of $ i $ . What is the minimum number of operations required to delete all elements from the multiset?

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