Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
When middle prut valley is the land formation what is the highest of which currently forests, km² ?

### Inputs:
table_name: table, columns: ['land formation', 'area, km²', 'of which currently forests, km²', '% forests', 'habitat type']

### Response:
SELECT MAX of which currently forests, km² FROM table WHERE land formation = Middle Prut Valley