Question 82
Magician puts on the $3 \times 100$ board cards with numbers from $1$ to $300$ in a "snake-like" line so that consecutive numbers are side-to-side adjacent (either horizontally or vertically, not diagonally). The numbers are written on the bottom sides of the cards, the upper sides are empty. After that the magician turns $k$ cards by his choice. For what minimum $k$ can it happen that open cards determine uniquely the whole snake?