===== ISTEM =====
Solve the following programming task.

TASK: Roman Numeral to Integer

Write a function 'roman_to_int(s)' that converts a valid Roman numeral string (I, V, X, L, C, D, M) to an integer. It must handle the rules IV=4, IX=9, XL=40, XC=90, CD=400, CM=900.

STARTER CODE (python):
def roman_to_int(s: str) -> int:
    # Write your code here
    pass


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```python
def roman_to_int(s: str) -> int:
    roman_map = {
        "I": 1,
        "V": 5,
        "X": 10,
        "L": 50,
        "C": 100,
        "D": 500,
        "M": 1000,
    }
    total = 0
    n = len(s)
    for i in range(n):
        val = roman_map[s[i]]
        if i + 1 < n and val < roman_map[s[i + 1]]:
            total -= val
        else:
            total += val
    return total
```