Given the sorted integer array citations, return the researcher’s h-index.

The h-index is the largest value h such that the researcher has at least h papers with at least h citations each.

Note: citations is sorted in ascending order.

Constraints:

• n == citations.length

• $1 \leq$ n $\leq 10^5$

• $0 \leq$ citations[i] $\leq 1000$

• citations is sorted in ascending order

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