#include <bits/stdc++.h>
inline int min(const int &first, const int &second) {
  return (((second - first) >> (32 - 1)) & (first ^ second)) ^ first;
}
inline int max(const int &first, const int &second) {
  return (((second - first) >> (32 - 1)) & (first ^ second)) ^ second;
}
inline long long min(const long long &first, const long long &second) {
  return (((second - first) >> (64 - 1)) & (first ^ second)) ^ first;
}
inline long long max(const long long &first, const long long &second) {
  return (((second - first) >> (64 - 1)) & (first ^ second)) ^ second;
}
using namespace std;
char string_in_buffer[(int)260];
void fast_scan(int &first) { scanf("%d", &first); }
void fast_scan(long long &first) { scanf("%lld", &first); }
void fast_scan(unsigned long long &first) { scanf("%llu", &first); }
void fast_scan(double &first) { scanf("%lf", &first); }
void fast_scan(long double &first) { scanf("%Lf", &first); }
void fast_scan(char &first) {
  scanf("%c", &first);
  if (first == '\n') {
    fast_scan(first);
  }
}
void fast_scan(string &first) {
  scanf("%s", string_in_buffer);
  first = string(string_in_buffer);
}
template <class TFirst, class TSecond>
void fast_scan(pair<TFirst, TSecond> &p) {
  fast_scan(p.first);
  fast_scan(p.second);
}
template <class T>
void fast_scan(vector<T> &v) {
  for (auto &first : v) fast_scan(first);
}
void fast_print(const int &first) { printf("%d", first); }
void fast_print(const unsigned int &first) { printf("%u", first); }
void fast_print(const long long &first) { printf("%lld", first); }
void fast_print(const unsigned long long &first) { printf("%llu", first); }
void fast_print(const char &first) { printf("%c", first); };
void fast_print(const double &first) { printf("%.15lf", first); }
void fast_print(const long double &first) { printf("%.15Lf", first); }
void fast_print(const string &first) { printf("%s", first.c_str()); }
void fast_print(const char v[]) { fast_print((string)v); }
template <class TFirst, class TSecond>
void fast_print(const pair<TFirst, TSecond> &p) {
  fast_print(p.first);
  fast_print(' ');
  fast_print(p.second);
}
template <class T>
void fast_print(const vector<T> &v) {
  if (v.empty()) return;
  fast_print(v[0]);
  for (int i = 1; i < v.size(); i++) {
    fast_print(' ');
    fast_print(v[i]);
  }
}
template <class T>
void fast_print(const vector<vector<T>> &v) {
  if (v.empty()) return;
  fast_print(v[0]);
  for (int i = 1; i < v.size(); i++) {
    fast_print('\n');
    fast_print(v[i]);
  }
}
template <class T>
void fast_print(const T &v) {
  for (const auto &first : v) {
    fast_print(first);
    fast_print(' ');
  }
}
using namespace std;
namespace smart_io {
string print_start = "";
string sep = " ";
bool first_print = false;
void precall_print() {
  fast_print(print_start);
  print_start = "\n";
  first_print = true;
}
void _print(deque<string>) {}
template <class T, class... Args>
void _print(deque<string> names, T elem, Args... args) {
  if (!first_print) {
    fast_print("\n");
  } else {
    first_print = false;
  }
  fast_print(names.front());
  fast_print(" = ");
  fast_print(elem);
  names.pop_front();
  _print(names, args...);
}
}  // namespace smart_io
template <class T>
ostream &operator,(ostream &os, const T &object) {
  if (!smart_io::first_print) {
    fast_print(smart_io::sep);
  } else {
    smart_io::first_print = false;
  }
  fast_print(object);
  return os;
}
template <class T>
istream &operator,(istream &is, T &object) {
  fast_scan(object);
  return is;
}
namespace escape__from__random__aetuhoetnuhshe {
using namespace std::chrono;
mt19937 rng(duration_cast<milliseconds>(system_clock::now().time_since_epoch())
                .count());
uniform_real_distribution<> prob_dist(0.0, 1.0);
};  // namespace escape__from__random__aetuhoetnuhshe
namespace typedefs {}
namespace numbers_operation {
template <class T>
inline T floor_mod(T a, const T &b) {
  a %= b;
  if (a < 0) a += b;
  return a;
}
}  // namespace numbers_operation
using namespace numbers_operation;
using namespace typedefs;
using namespace escape__from__random__aetuhoetnuhshe;
int n, m;
vector<vector<pair<int, int>>> g;
vector<bool> used;
vector<int> st;
vector<int> type;
bool dfs(int v, int cur, int req) {
  st.push_back(v);
  used[v] = true;
  type[v] = cur;
  for (pair<int, int> sub : g[v]) {
    if (used[sub.first]) {
      if ((type[sub.first] ^ type[v] ^ sub.second) != req) {
        return false;
      }
    } else {
      if (!dfs(sub.first, type[v] ^ sub.second ^ req, req)) return false;
    }
  }
  return true;
}
signed main(signed argc, char *argv[]) {
  cin, n, m;
  g.resize(n);
  type.resize(n);
  for (int i = 0; i < (m); i++) {
    int a, b;
    string c;
    cin, a, b;
    cin, c;
    a--;
    b--;
    g[a].emplace_back(b, c == "R");
    g[b].emplace_back(a, c == "R");
  }
  vector<int> final(n + 1, -1);
  for (int req = 0; req < 2; req++) {
    vector<int> full;
    used = vector<bool>(n, false);
    for (int i = 0; i < (n); i++) {
      if (used[i]) continue;
      vector<int> best{-1};
      for (int d = 0; d < (2); d++) {
        st.clear();
        if (dfs(i, d, req)) {
          vector<int> acts;
          for (int first : st) {
            if (type[first]) acts.push_back(first);
          }
          if (best == vector<int>{-1} ||
              ((int)best.size()) > ((int)acts.size())) {
            best = acts;
          }
        }
        if (d == 0)
          for (int first : st) {
            used[first] = false;
          }
      }
      if (best == vector<int>{-1}) best = vector<int>(n + 1, -1);
      full.insert(full.end(), best.begin(), best.end());
      if (((int)full.size()) > n) break;
    }
    if (((int) final.size()) > ((int)full.size())) final = full;
  }
  if (((int) final.size()) <= n) {
    smart_io::precall_print();
    cout, ((int) final.size());
    for (auto &first : final) {
      first++;
    };
    smart_io::precall_print();
    cout, final;
  } else {
    smart_io::precall_print();
    cout, -1;
  }
}
