def _capitalize_first_letter(c):
    """Capitalize the first letter of the input.

    Unlike the built-in capitalize() method, doesn't lower-case the other
    characters.  This helps mimic the behavior of proto-lens-protoc, which turns
    Foo/Bar/BAZ.proto into Foo/Bar/BAZ.hs (rather than Foo/Bar/Baz.hs).

    Args:
      c: A non-empty string word.

    Returns:
      The input with the first letter upper-cased.
    """
    return c[0].capitalize() + c[1:]