Cutting Plants

Daniil is a royal gardener. He takes care of a garden with $N$ plants numbered $1$ through $N$. For each $i$ ($1 \le i \le N$), the initial height of the $i$-th plant is $A_i$. Unfortunately, the Queen doesn't like the garden, so she asked Daniil to cut some plants — in order to satisfy the Queen's request, the $i$-th plant should have height $B_i$ (for each $1 \le i \le N$). Daniil is allowed to