{"problem":{"name":"K. Keep Calm and Sell Balloons","description":{"content":"The complete problemset is available on http://maratona.ime.usp.br/primfase19/provas/competicao/maratona_en.pdf ","description_type":"Markdown"},"platform":"Codeforces","limit":{"time_limit":1000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"CF10234K"},"statements":[{"statement_type":"Markdown","content":"The complete problemset is available on http://maratona.ime.usp.br/primfase19/provas/competicao/maratona_en.pdf\n\n[samples]","is_translate":false,"language":"English"},{"statement_type":"Markdown","content":"**Definitions**  \nLet $ n \\in \\mathbb{Z} $ be even, $ 2 \\leq n \\leq 50 $.  \nThe wall is an $ n \\times n $ grid. Position $ (i, j) $ must contain:  \n- Stone block if $ i + j \\equiv 0 \\pmod{2} $,  \n- Sand block if $ i + j \\equiv 1 \\pmod{2} $.  \n\n**Constraints**  \n- Only two operations allowed:  \n  1. Place a single block of correct type on a *free* position.  \n  2. Fill all empty positions in a $ 2 \\times 2 $ square with a single block type, provided at least one position in the square is *free* and the entire square lies within bounds ($ 1 \\leq x, y \\leq n-1 $).  \n- No block may be placed in a position where its type contradicts the chequered pattern.  \n- Total operations $ k \\leq \\frac{3n^2}{4} $.  \n\n**Objective**  \nConstruct a sequence of operations (each of type 1 or 2) that fills the grid according to the chequered pattern, using at most $ \\frac{3n^2}{4} $ operations.","is_translate":false,"language":"Formal"}],"meta":{"iden":"CF10234K","tags":[],"sample_group":[],"created_at":"2026-03-03 11:00:39"}}