CF218A Mountain Scenery

Little Bolek has found a picture with $ n $ mountain peaks painted on it. The $ n $ painted peaks are represented by a non-closed polyline, consisting of $ 2n $ segments. The segments go through $ 2n+1 $ points with coordinates $ (1,y_{1}) $ , $ (2,y_{2}) $ , $ ... $ , $ (2n+1,y_{2n+1}) $ , with the $ i $ -th segment connecting the point $ (i,y_{i}) $ and the point $ (i+1,y_{i+1}) $ . For any even $ i $ $ (2

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