CF750E New Year and Old Subsequence

A string $ t $ is called nice if a string "2017" occurs in $ t $ as a subsequence but a string "2016" doesn't occur in $ t $ as a subsequence. For example, strings "203434107" and "9220617" are nice, while strings "20016", "1234" and "20167" aren't nice. The ugliness of a string is the minimum possible number of characters to remove, in order to obtain a nice string. If it's impossible to make a string nice by removing characters, its ugliness is $ -1 $ . Limak has a string $ s $ of length $ n $ , with characters indexed $ 1 $ through $ n $ . He asks you $ q $ queries. In the $ i $ -th query you should compute and print the ugliness of a substring (continuous subsequence) of $ s $ starting at the index $ a_{i} $ and ending at the index $ b_{i} $ (inclusive).

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In the first sample: - In the first query, $ ugliness( $ "20166766" $ )=4 $ because all four sixes must be removed. - In the second query, $ ugliness( $ "2016676" $ )=3 $ because all three sixes must be removed. - In the third query, $ ugliness( $ "0166766" $ )=-1 $ because it's impossible to remove some digits to get a nice string. In the second sample: - In the second query, $ ugliness( $ "01201666209167" $ )=2 $ . It's optimal to remove the first digit '2' and the last digit '6', what gives a string "010166620917", which is nice. - In the third query, $ ugliness( $ "016662091670" $ )=1 $ . It's optimal to remove the last digit '6', what gives a nice string "01666209170".