def int_to_roman(n):
    if not isinstance(n, int) or isinstance(n, bool) or n < 1 or n > 3999:
        raise ValueError(f"Input must be an integer in range 1..3999, got {n!r}")

    values = [
        1000, 900, 500, 400,
        100,   90,  50,  40,
        10,     9,   5,   4,
        1,
    ]
    symbols = [
        'M',  'CM', 'D', 'CD',
        'C',  'XC', 'L', 'XL',
        'X',  'IX', 'V', 'IV',
        'I',
    ]

    result = []
    for value, symbol in zip(values, symbols):
        while n >= value:
            result.append(symbol)
            n -= value
    return ''.join(result)


def roman_to_int(s):
    if not s:
        raise ValueError("Empty string is not a valid Roman numeral")

    roman_vals = {
        'I': 1, 'V': 5, 'X': 10, 'L': 50,
        'C': 100, 'D': 500, 'M': 1000,
    }

    for ch in s:
        if ch not in roman_vals:
            raise ValueError(f"Invalid character {ch!r} in Roman numeral {s!r}")

    total = 0
    prev = 0
    for ch in reversed(s):
        curr = roman_vals[ch]
        if curr < prev:
            total -= curr
        else:
            total += curr
        prev = curr

    if total < 1 or total > 3999:
        raise ValueError(f"Roman numeral {s!r} evaluates to {total}, out of range 1..3999")

    canonical = int_to_roman(total)
    if canonical != s:
        raise ValueError(
            f"{s!r} is not a canonical Roman numeral (canonical form is {canonical!r})"
        )

    return total