algebra precalculus - Polynomials, prove exercise question about question

There is a polynomial P with integer coefficients and with pairwise different integers $a,b,c$ . Prove that it is not possible for $P(a) = b$, $P(b)=c$, $P(c) = a$

First off I don't understand "pairwise different" part - what does it mean ,can you show me this as an equation? After that I'd like to get a hint in case I don't make it. + I'd prefer to have hints/answers written more algebraically without $\sum$ etc. (It helps me get better understanding what's going on under the hood)