Saitama: "The Hero Association called me for a low-level mission, can you meet them as my representative?"
Saitama: "Aww, man.. That's not fun."
Then Saitama decided to meet Hero Association.
The world of One Punch Man consists of exactly 25 cities labeled $A$ to $Y$ (there used to be a city labeled $Z$, but it is abandoned and we will not use it in this puzzle). Each pair of cities are connected by a road hence there are 300 roads in total. Hero Association wants Saitama to plan a patrolling strategy.
There are 100 heroes (a.k.a riders) that will cycle their bike to patrol along their planned route each night. To make it happened, Hero Association wants to make 100 Triangle of Safety. Triangle of Safety is defined as a set of 3 different cities which has a road connecting each pair of them, i.e. a cycle of 3 cities, which will be a route for a patrolling rider. Obviously, these 100 Triangle of Safety must cover all roads.
This mission is, of course, really boring for Saitama. Can you help him to determine one of the possible configuration for 100 Triangle of Safety, or prove that it is an impossible mission?
This puzzle is based on a competitive programming problem authored by me. It is used in Indonesia National Contest 2017, a qualification round of The ACM International Collegiate Programming Contest (ICPC) Asia Jakarta 2017. The link of the problem is here.