RIOPLATENSE 1996 Problem 2

A magic square is a table in which all the natural numbers from $1$ to $16$ appear and such that: $\bullet$ all rows have the same sum $s$ . $\bullet$ all columns have the same sum $s$ . $\bullet$ both diagonals have the same sum $s$ . It is known that $a_{22} = 1$ and $a_{24} = 2$ . Calculate $a_{44}$ .