How many insurgents are there when the total per period is 156?
CREATE TABLE table_24521 (
    "Period" real,
    "Civilians" text,
    "Security forces" text,
    "Insurgents" text,
    "Total per period" real
)
SELECT "Insurgents" FROM table_24521 WHERE "Total per period" = '156'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How many insurgents are there when the total per period is 156? ### Input: CREATE TABLE table_24521 (
    "Period" real,
    "Civilians" text,
    "Security forces" text,
    "Insurgents" text,
    "Total per period" real
) ### Response: SELECT "Insurgents" FROM table_24521 WHERE "Total per period" = '156'