Graph Coloring

Description:

Input:

The first line of the input contains two integers n and m (1 ≤ n, m ≤ 100 000) — the number of vertices and edges, respectively.

The following m lines provide the description of the edges, as the i-th of them contains two integers u_i and v_i (1 ≤ u_i, v_i ≤ n, u_i ≠ v_i) — the indices of the vertices connected by the i-th edge, and a character c_i () providing the initial color of this edge. If c_i equals 'R', then this edge is initially colored red. Otherwise, c_i is equal to 'B' and this edge is initially colored blue. It's guaranteed that there are no self-loops and multiple edges.

Output:

If there is no way to make the colors of all edges equal output  - 1 in the only line of the output. Otherwise first output k — the minimum number of moves required to achieve the goal, then output k integers a₁, a₂, ..., a_k, where a_i is equal to the index of the vertex that should be used at the i-th move.

If there are multiple optimal sequences of moves, output any of them.

Sample Input:

3 3
1 2 B
3 1 R
3 2 B

Sample Output:

1
2 

Sample Input:

6 5
1 3 R
2 3 R
3 4 B
4 5 R
4 6 R

Sample Output:

2
3 4 

Sample Input:

4 5
1 2 R
1 3 R
2 3 B
3 4 B
1 4 B

Sample Output:

-1