problem: For the arithmetic sequence $1000, ~987, ~974, ~961, \ldots ,$ what is the least positive integer in the sequence?
solution: The common difference in this arithmetic sequence is $987 - 1000= -13$, so the $n^{\text{th}}$ term in this sequence is $1000 - 13(n - 1) = 1013 - 13n$.  This expression is positive if and only if $1013 - 13n > 0$, or \[n < \frac{1013}{13} = 77 + \frac{12}{13}.\] Since $n$ must be a positive integer, $n \le 77$.  Hence, the least positive integer in this sequence corresponds to the value $n = 77$, in which case $1013 - 13n = 1013 - 13 \cdot 77 = \boxed{12}$.