Find the number of ways to place one math book and one science book in a row on a bookshelf.
[OP_LIST_SOL] math science [OP_LIST_EOL] [OP_LIST_LEN] [OP_LIST_LEN] [OP_PERM]
var_a = 'math'
var_b = 'science'
list_a= []
if "/" in str(var_b):
    var_b = eval(str(var_b))
list_a.append(var_b)
if "/" in str(var_a):
    var_a = eval(str(var_a))
list_a.append(var_a)
list_a.reverse()
var_c = len(list_a)
var_d = len(list_a)
var_e = 1
var_c = int(var_c)
var_d = int(var_d)
for i, elem in enumerate(range(var_d)):
    var_e = var_e * (var_c-i)
print(int(var_e))