How many insurgent is it when total period 156?
Period Civilians Security forces Insurgents Total per period
real text text text real
1-21636599-2
1996 N/A N/A N/A 156
1997 202 44 102 348
1998 118 42 110 270
1999 115 36 212 363
2000 N/A N/A N/A 50
2001 N/A N/A N/A 564
table_21636599_2
SELECT Insurgents FROM table WHERE Total per period = 156
156