#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
template <typename T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T, class T1>
inline void gn(T &first, T1 &second) {
  gn(first);
  gn(second);
}
template <class T, class T1, class T2>
inline void gn(T &first, T1 &second, T2 &z) {
  gn(first);
  gn(second);
  gn(z);
}
template <typename T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <typename T>
inline void println(T first) {
  print(first), putchar('\n');
}
template <typename T>
inline void printsp(T first) {
  print(first), putchar(' ');
}
template <class T, class T1>
inline void print(T first, T1 second) {
  printsp(first), println(second);
}
template <class T, class T1, class T2>
inline void print(T first, T1 second, T2 z) {
  printsp(first), printsp(second), println(z);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
vector<pair<int, int> > adj[100100];
int n, m;
pair<pair<int, int>, int> edge[100100];
int col[100100];
vector<int> vec[2];
bool dfs(int u, int c = 0) {
  col[u] = c;
  vec[c].push_back(u);
  for (int i = 0; i < adj[u].size(); i++) {
    int v = adj[u][i].first;
    if (col[v] != -1) {
      if (col[v] == col[u] && adj[u][i].second) return false;
      if (col[v] != col[u] && !adj[u][i].second) return false;
      continue;
    }
    if (!dfs(v, c ^ adj[u][i].second)) return false;
  }
  return true;
}
vector<int> ids;
int solve(int tp) {
  for (int i = 1; i <= n; i++) adj[i].clear(), col[i] = -1;
  for (int i = 0; i < m; i++) {
    int u = edge[i].first.first;
    int v = edge[i].first.second;
    adj[u].push_back(pair<int, int>(v, edge[i].second == tp));
    adj[v].push_back(pair<int, int>(u, edge[i].second == tp));
  }
  ids.clear();
  for (int i = 1; i <= n; i++)
    if (col[i] == -1) {
      vec[0].clear();
      vec[1].clear();
      if (!dfs(i)) return 0x3f3f3f3f;
      int tp = vec[0].size() > vec[1].size();
      for (int j = 0; j < vec[tp].size(); j++) ids.push_back(vec[tp][j]);
    }
  return ids.size();
}
int main() {
  gn(n, m);
  for (int i = 0; i < m; i++) {
    int u, v;
    char c;
    gn(u, v);
    scanf(" %c", &c);
    edge[i] = pair<pair<int, int>, int>(pair<int, int>(u, v), c == 'R');
  }
  int ans = solve(0);
  vector<int> res = ids;
  int tmp = solve(1);
  if (tmp < ans) ans = tmp, res = ids;
  if (ans < 0x3f3f3f3f) {
    println(ans);
    for (int i = 0; i < res.size(); i++) printsp(res[i]);
    puts("");
  } else
    puts("-1");
  return 0;
}
