Given two positive integers $a$ and $b$, an legal move consists in choosing a proper divisor of one of them and adding it to $a$ or adding it to $b$. Two players, Agustin and Ian, take turns making an legal move; Agustin plays first. Whoever gets a number greater than or equal to $2015$ wins the game. Determine which of the players has a winning strategy if $a=3, b=5$. Determine which of the players has a winning strategy if $a=6, b=7$.