The problem can be found here: https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=4878
I know the final answer but idk how to get it myself.
How to solve UVA12995 — Farey Sequence
The problem can be found here: https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=4878