Školjka

%V0 Let $n$ be a positive integer. How many integer solutions $(i, j, k, l) , \ 1 \leq i, j, k, l \leq n$, does the following system of inequalities have: $$1 \leq -j + k + l \leq n$$ $$1 \leq i - k + l \leq n$$ $$1 \leq i - j + l \leq n$$ $$1 \leq i + j - k \leq n \ ?$$