CF140C New Year Snowmen

As meticulous Gerald sets the table and caring Alexander sends the postcards, Sergey makes snowmen. Each showman should consist of three snowballs: a big one, a medium one and a small one. Sergey's twins help him: they've already made $ n $ snowballs with radii equal to $ r_{1} $ , $ r_{2} $ , ..., $ r_{n} $ . To make a snowman, one needs any three snowballs whose radii are pairwise different. For example, the balls with radii $ 1 $ , $ 2 $ and $ 3 $ can be used to make a snowman but $ 2 $ , $ 2 $ , $ 3 $ or $ 2 $ , $ 2 $ , $ 2 $ cannot. Help Sergey and his twins to determine what maximum number of snowmen they can make from those snowballs.

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