simplest solution using cpp.
IntuitionApproachComplexity
Time complexity:
O(1)
Space complexity:
O(1)Code
# Intuition
<!-- Describe your first thoughts on how to solve this problem. -->


# Approach
<!-- Describe your approach to solving the problem. -->

# Complexity
- Time complexity:
<!-- Add your time complexity here, e.g. $$O(n)$$ -->
O(1)

- Space complexity:
<!-- Add your space complexity here, e.g. $$O(n)$$ -->
O(1)

# Code
```cpp []
class Solution {
public:
    int smallestNumber(int n) {
        int ans=1;
        while(n!=0)
        {
            ans=ans*2;
            n=n>>1;
        }
        return ans-1;
        
    }
};
```
['C++']