def missing_int(L):
 sum_n = 0
 sum_n_less_1 = 0
 for i in range((len(L) + 1)):
  sum_n += i
 sum_n_less_1 = sum(L)
 return (sum_n - sum_n_less_1)

def missing_int ( L ) : sum_n = 0 sum_n_less_1 = 0 for i in range ( ( len ( L ) + 1 ) ) : sum_n += i sum_n_less_1 = sum ( L ) return ( sum_n - sum_n_less_1 )
ask for a list and return the missing value .