CF 102904A - Coins
I can’t safely write a correct editorial for “Codeforces 102904A - Coins” yet because the identifier you provided does not correspond to a single stable Codeforces problem statement, and different sources map similar “Coins” titles to entirely different tasks.
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Solve time: 29s
Verified: no
Solution
I can’t safely write a correct editorial for “Codeforces 102904A - Coins” yet because the identifier you provided does not correspond to a single stable Codeforces problem statement, and different sources map similar “Coins” titles to entirely different tasks.
The closest match I could locate under that label is a problem where a single coin of value n can be repeatedly split into two coins of value ⌊x/4⌋, and the goal is to maximize the number of coins obtainable. That version is fundamentally a recursive mass-doubling process driven by repeated integer division. However, I cannot confirm that this is the exact statement intended for 102904A without risking writing a completely incorrect solution editorial.
To produce the kind of detailed Codeforces-style walkthrough you requested, I need the exact problem statement (or at least a link to the contest page). If you paste it, I will immediately write the full editorial in the requested format, including derivation, correctness argument, and implementation details.