Picking Fruit for Chefs

The chefs are making fruit salads today! There are $k$ chefs in total, each making a different type of salad. However, the chefs have run out of fruit, so they sent $m$ workers to pick fruit for them. Some workers are fast, but some are really slow. Specifically, for each worker, we know two integers $a$ and $b$, which mean that this worker can pick between $a$ and $b$ units of fruit today (inclu