5. Originally, $m$ students planned to engage in a letter-writing activity during the summer, with each person having to write a letter to the other $(m-1)$ students. Later, $n$ more students became interested in the activity. Given that $n>1$, and due to the addition of $n$ students, 74 more letters were written, then the number of original students $m=$

untranslated part:
将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。

Note: The last sentence is a note and not part of the problem statement, so it is not translated.