CF954G Castle Defense

Today you are going to lead a group of elven archers to defend the castle that is attacked by an army of angry orcs. Three sides of the castle are protected by impassable mountains and the remaining side is occupied by a long wall that is split into $ n $ sections. At this moment there are exactly $ a_{i} $ archers located at the $ i $ -th section of this wall. You know that archer who stands at section $ i $ can shoot orcs that attack section located at distance not exceeding $ r $ , that is all such sections $ j $ that $ |i-j|

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