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

### Instruction:
How many cities had a census of 400000 in 1940?

### Inputs:
table_name: table, columns: ['Rank', 'City', '1890 census', '1910 census', '1920 census', '1930 census', '1940 census']

### Response:
SELECT COUNT Rank FROM table WHERE 1940 census = 400000