from typing import Dict


def formula_dict_to_elements(formula: Dict[str, int]) -> str:
    """
    Converts a sum formula from a dictionary like {'C': 12, 'H': 6, 'O': 3} to a
    string like C H O.
    >>> formula_dict_to_elements({'Elem_C': 12, 'Elem_H': 6.5, 'Elem_O': 3, 'Elem_Mn': 7})
    'C H O Mn'
    >>> formula_dict_to_elements({'Elem_C': 12, 'Elem_H': 6.5, 'Elem_O': 3, 'Elem_Mn': 7, 'Elem_N': 0})
    'C H O Mn'
    """
    formstr = ' '.join([x[5:] for x in formula.keys() if formula[x]])
    return formstr