[*] Putnam A3 문제 풀이

[Limax314]

Is your feature request related to a problem? Please describe.

• A3 문제 풀이

Describe the solution you'd like

• Lean 또는 LaTeX를 이용하여 문제 및 논리적 비약없는 풀이 정리.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

• 참고 자료: