def sum_series(n):
  
  if n < 1:
    return 0
  else:
    return n + sum_series(n - 2)
def sum_series(n):
    if n < 1:
        _i_2 = 0
        if _i_2 < _i_2:
            return n + sum_series(n - 2)
       
        return 0
    else:
        return n + sum_series(n - 2)