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

### Instruction:
What is the sum of the serial numbers for narowal city?

### Inputs:
table_name: table, columns: ['Serial No.', 'District', 'Headquartered City', 'City Population (2009)', 'City Area(km 2 )']

### Response:
SELECT SUM Serial No. FROM table WHERE Headquartered City = narowal city