input: Write a function to calculate the sum of a sequence of integers. If the given sequence is empty, return 0.
  assert sum_sequence([1, 2, 3, 4, 5])==15
  assert sum_sequence([-1, -2, -3, -4, -5])==-15
  assert sum_sequence([0, 0, 0, 0, 0])==0
  assert sum_sequence([10])==10
  assert sum_sequence([])==0
output: def sum_sequence(sequence):
      return sum(sequence)