Problem

Source: 2022 Polish Junior Math Olympiad Finals P1

Tags: geometry



Given is a square $ABCD$ with side length $1$. Points $K$, $L$, $M$, and $N$, distinct from the vertices of the square, lie on segments $AB$, $BC$, $CD$, and $DA$, respectively. Prove that the perimeter of at least one of the triangles $ANK$, $BKL$, $CLM$, $DMN$ is less than $2$.