Problem - Minimum Waiting Time

$n$ people wait in line. Person $i$ takes $t_i$ time to be served. Minimize total waiting time (sum of all waiting times).

Example: times = [3, 2, 1]. If order is [3, 2, 1]: person $1$ waits $0$, person $2$ waits $3$, person $3$ waits $3$ + $2$ = $5$. Total: $0$ + $3$ + $5$ = $8$. If order is [1, 2, 3]: person $1$ waits $0$, person $2$ waits $1$, person $3$ waits $1$ + $2$ = $3$. Total: $0$ + $1$ + $3$ = $4$. Better!

What is the optimal order? Can you prove it? The order you choose affects everyone behind.