Ants and Anteaters

You are given a grid with $R$ rows (numbered $1$ through $R$) and $C$ columns (numbered $1$ through $C$). Initially, each cell of this grid is either empty, contains an ant or an anteater. Each ant is moving in a fixed direction: up, down, left or right. The anteaters do not move. The movement of ants happens in discrete steps. For example, when an ant is in the cell in the $i$-th row and $j$-th