Editorial for COCI '16 Contest 5 #3 Unija

Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.

It is enough to observe only the right half of the image and in the end double the result. The solution is to sum the heights of $X$ ~X~-columns for $X = 1, 2, \dots, 10^7$ ~X = 1, 2, \dots, 10^7~, which can be done using a for loop.

How to determine the height of the column at coordinate $X$ ~X~? It is larger than or equal to the height of column at coordinate $X+1$ ~X+1~. It is larger if a rectangle exists that ends at coordinate $X$ ~X~ and is higher than the column at coordinate $X+1$ ~X+1~, otherwise it is equal. Therefore, initially, we need to store the $X$ ~X~-coordinates where the given rectangles end and their heights, then traverse the $X$ ~X~-columns "backwards", towards the beginning, in order to apply the aforementioned formula.

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