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

### Instruction:
What Nature reserve number was established on 19961220 20.12.1996

### Inputs:
table_name: table, columns: ['NSG Nr.', 'Name of the nature reserve', 'District / Town', 'Area (ha)', 'Date established']

### Response:
SELECT MIN NSG Nr. FROM table WHERE Date established = 19961220 20.12.1996