PAMO 2016 Q6
Source: PAMO 2016
April 29, 2016
combinatoricssquare gridparallelogram
Problem Statement
Consider an grid formed by unit squares. We define the centre of a unit square as the intersection of its diagonals.
Find the smallest integer such that, choosing any unit squares in the grid, we always get four unit squares among them whose centres are vertices of a parallelogram.