Let $N$ be a positive integer. It is given set of weights which satisfies following conditions: $i)$ Every weight from set has some weight from $1,2,...,N$; $ii)$ For every $i\in {1,2,...,N}$ in given set there exists weight $i$; $iii)$ Sum of all weights from given set is even positive integer. Prove that set can be partitioned into two disjoint sets which have equal weight