CF1442A Extreme Subtraction

You are given an array $ a $ of $ n $ positive integers. You can use the following operation as many times as you like: select any integer $ 1 \le k \le n $ and do one of two things: - decrement by one $ k $ of the first elements of the array. - decrement by one $ k $ of the last elements of the array. For example, if $ n=5 $ and $ a=[3,2,2,1,4] $ , then you can apply one of the following operations to it (not all possible options are listed below): - decrement from the first two elements of the array. After this operation $ a=[2, 1, 2, 1, 4] $ ; - decrement from the last three elements of the array. After this operation $ a=[3, 2, 1, 0, 3] $ ; - decrement from the first five elements of the array. After this operation $ a=[2, 1, 1, 0, 3] $ ; Determine if it is possible to make all the elements of the array equal to zero by applying a certain number of operations.

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