------
## 最终结论
```python
def common_prefix(strings, n):
    if not strings:
        return ""
    
    prefix = strings[0]
    
    for string in strings[1:]:
        while not string.startswith(prefix):
            prefix = prefix[:-1]
            if not prefix:
                return ""
    
    return prefix

# Test cases
assert common_prefix(["tablets", "tables", "taxi", "tamarind"], 4) == 'ta'
assert common_prefix(["apples", "ape", "april"], 3) == 'ap'
assert common_prefix(["teens", "teenager", "teenmar"], 3) == 'teen'
```