Resolve left-rescursion

Question

Can anybody give me a hint on how to get rid of the left recursion in the following grammar?

$$A \rightarrow B \mid a$$ $$B \rightarrow b \mid C \mid D \mid E \mid F \mid G$$ $$C \rightarrow c \mid A d$$ $$D \rightarrow A e \mid f$$ $$E \rightarrow g \mid B h$$ $$F \rightarrow i \mid A j \mid k$$ $$G \rightarrow l \mid A m \mid n$$

So far I've tried this algorithm and this tool. But both are only applicable for smaller grammars and provide practically unusable results (1000's of rules).