\section*{Problem 7}

What is the largest possible value of \(|\ldots|\left|a_{1}-a_{2}\right|-a_{3}\left|-\ldots-a_{1990}\right|\), where \(\mathrm{a}_{1}, a_{2}, \ldots, a_{1990}\) is a permutation of \(1,2,3, \ldots, 1990\) ?

Answer \(\quad 1989\)