------
## 最终结论
```python
def remove_lowercase(s):
    result = ""
    for char in s:
        if char.isupper():
            result += char
    return result

# Test cases
assert remove_lowercase("PYTHon") == 'PYTH'
assert remove_lowercase("FInD") == 'FID'
assert remove_lowercase("STRinG") == 'STRG'
```