CF367D Sereja and Sets

Sereja has $ m $ non-empty sets of integers $ A_{1},A_{2},...,A_{m} $ . What a lucky coincidence! The given sets are a partition of the set of all integers from 1 to $ n $ . In other words, for any integer $ v $ $ (1

The first line contains integers $ n $ , $ m $ , $ d $ $ (1

In a single line print the answer to the problem — the minimum value $ k $ at the right choice.