Gar the Magician wrote each of the numbers from $1$ to $7$, one on
each of seven cards, and placed them in his hat. He offered the hat
to two other magicians, Kan and Roo. Kan took, at random, $3$ cards
from the hat and Roo took $2$ cards (so that there were $2$ cards
left in the hat). Kan told Roo: "I can deduce that the sum of the
numbers of your cards is even". What was the sum of the numbers on
Kan's cards?