20 ducks are waiting their turn to drink. If 11 ducks drank before the (a) duck, how many ducks drank after the (a) duck?
20 11 [OP_SUB] 1 [OP_SUB]
var_a = 20
var_b = 11
var_c = var_a - var_b
var_d = 1
var_e = var_c - var_d
print(int(var_e))