#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
const int maxn = 1e5 + 5;
vector<pair<int, int> > V[maxn];
int color[maxn];
vector<int> num[3];
bool dfs(int u, int c, int flag) {
  color[u] = c;
  num[c].push_back(u);
  for (auto e : V[u]) {
    int v = e.first;
    int f = e.second;
    if (color[v] != -1) {
      if ((f ^ flag) == 0 && color[u] != color[v]) {
        return false;
      } else if ((f ^ flag) == 1 && color[u] == color[v]) {
        return false;
      }
    } else {
      if ((f ^ flag) == 0) {
        bool check = dfs(v, c, flag);
        if (!check) return false;
      } else {
        bool check = dfs(v, c ^ 1, flag);
        if (!check) return false;
      }
    }
  }
  return true;
}
int n, m;
vector<int> work(int flag) {
  vector<int> ans;
  memset(color, -1, sizeof(color));
  for (int i = 1; i <= n; i++) {
    if (color[i] == -1) {
      num[0].clear();
      num[1].clear();
      bool f = dfs(i, 0, flag);
      if (!f) {
        for (int i = 1; i <= n + 1; i++) {
          ans.push_back(1);
        }
        return ans;
      }
      int chose = 0;
      if (num[0].size() > num[1].size()) {
        chose = 1;
      }
      for (int j = 0; j < num[chose].size(); j++) {
        ans.push_back(num[chose][j]);
      }
    }
  }
  return ans;
}
int main() {
  scanf("%d %d", &n, &m);
  int u, v;
  char s;
  for (int i = 1; i <= m; i++) {
    scanf("%d %d %c", &u, &v, &s);
    int flag = (s == 'B');
    V[u].push_back({v, flag});
    V[v].push_back({u, flag});
  }
  vector<int> ans = work(0);
  vector<int> ans2 = work(1);
  if (ans.size() > n && ans2.size() > n) {
    puts("-1");
    return 0;
  }
  if (ans.size() > ans2.size()) {
    swap(ans, ans2);
  }
  cout << ans.size() << endl;
  for (auto v : ans) {
    printf("%d ", v);
  }
  puts("");
  return 0;
}
