Uniform

In a school, there are $C$ clubs (numbered $1$ through $C$) that students can participate in. Each student can be in zero, one or multiple clubs. Tomorrow, there is a school assembly and $N$ students (numbered $1$ through $N$) will be standing in a line. Each student should wear one of $M$ single-colour shirts provided by the school. The only restriction is that for each club, students in this