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

### Instruction:
What is the of Fleet size with a IATA of pr, and a Commenced operations smaller than 1941?

### Inputs:
table_name: table, columns: ['Airline', 'ICAO', 'IATA', 'Callsign', 'Commenced operations', 'Fleet size', 'Headquarters']

### Response:
SELECT SUM Fleet size FROM table WHERE IATA = pr AND Commenced operations < 1941