Given a set $S = {1, 2, \ldots, n}$, the task is to list all subsets of size $k$ in lexicographic order.
### Input
- A single line contains two integers $n,k$.
### Output
- List all subsets of size $k$ from set $S$ in lexicographic order.
### Constraints
- $1 \le k \le n \le 20$.
### Example
Input:
```
4 2
```
Output:
```
1 2
1 3
1 4
2 3
2 4
3 4
```
