55 students participated in A competition and B competition. Among them, 38 students participated in A  competition, and 42 students participated in B competition. If no student did not participate in neither competitions A nor B, how many students participated in both competitions?
38 42 [OP_ADD] 55 [OP_SUB]
var_a = 38
var_b = 42
var_c = var_a + var_b
var_d = 55
var_e = var_c - var_d
print(int(var_e))