Greenhouse and Plants

You have a Greenhouse of height $x$ units (i.e plants with height > $x$ cannot be kept inside it) and $n$ plants whose initial heights are $h_1, h_2…,h_n$. These plants are of a special kind: they grow by 1 unit if watered. You have to keep these plants in the greenhouse for at most $d$ days. On the $i$’th day, you have to water exactly $a_i$ different plants. You need to output the maximum num