------
## 最终结论
```python
def odd_values_string(s):
    return ''.join([s[i] for i in range(len(s)) if i % 2 == 0])

# Test cases
assert odd_values_string('abcdef') == 'ace'
assert odd_values_string('python') == 'pto'
assert odd_values_string('data') == 'dt'
```