Essentially, if you place the $n$ individuals at the vertices of an $n$-sided polygon and let the information circulate, the last two people ($n-1$ and $n$) will eventually know everything and must now share it with the remaining $(n-2)$ individuals. The process involves $(n-1)$ talks to spread the news around the polygon and then $(n-2)$ additional talks to inform the rest. In total, this results in $2n-3$ talks.