#include <bits/stdc++.h>
using namespace std;
void getre() {
  int x = 0;
  printf("%d\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1) res <<= 1;
  printf("%d\n", res);
}
template <typename T, typename S>
inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S>
inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN>
inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN>
inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N>
N gcd(N a, N b) {
  return b ? gcd(b, a % b) : a;
}
template <typename N>
inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9') x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
inline long long sqr(long long a) { return a * a; }
inline double sqrf(double a) { return a * a; }
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265358979323846264338327950288L;
const double eps = 1e-6;
const int mo = 1;
int qp(int a, long long b) {
  int n = 1;
  do {
    if (b & 1) n = 1ll * n * a % mo;
    a = 1ll * a * a % mo;
  } while (b >>= 1);
  return n;
}
struct ed {
  int u, v, d;
  void read() {
    gn(u);
    gn(v);
    char c;
    gc(c);
    if (c == 'B')
      d = 0;
    else
      d = 1;
  }
} e[111111];
int n, m;
int mi = inf;
vector<int> an;
int fa[322222];
int xa[222222], xb[222222];
int gf(int x) { return x == fa[x] ? x : fa[x] = gf(fa[x]); }
void un(int x, int y) {
  x = gf(x);
  y = gf(y);
  if (x != y) {
    fa[x] = y;
  }
}
int ne[222222];
void work(int d) {
  memset((xa), (0), sizeof(xa));
  memset((xb), (0), sizeof(xb));
  for (int i = (1), _ed = (3 * n + 1); i < _ed; i++) fa[i] = i;
  for (int i = (1), _ed = (m + 1); i < _ed; i++) {
    int u = e[i].u, v = e[i].v;
    if (d == e[i].d) {
      un(u, v);
      un(u + n, v + n);
    } else {
      un(u, v + n);
      un(v, u + n);
    }
    un(u + 2 * n, v + 2 * n);
  }
  for (int i = (1), _ed = (n + 1); i < _ed; i++)
    if (gf(i) == gf(i + n)) return;
  for (int i = (1), _ed = (n + 1); i < _ed; i++) {
    int r = gf(i + 2 * n) - 2 * n;
    if (gf(i) == gf(r))
      xa[r]++;
    else
      xb[r]++;
  }
  int su = 0;
  for (int i = (1), _ed = (n + 1); i < _ed; i++) {
    su += min(xa[i], xb[i]);
    ne[i] = xa[i] < xb[i];
  }
  if (su < mi) {
    mi = su;
    an.clear();
    for (int i = (1), _ed = (n + 1); i < _ed; i++) {
      int r = gf(i + 2 * n) - 2 * n;
      if ((gf(i) == gf(r)) == ne[r]) an.push_back(i);
    }
  }
}
int main() {
  gn(n);
  gn(m);
  for (int i = (1), _ed = (m + 1); i < _ed; i++) e[i].read();
  for (int d = 0; d <= 1; d++) work(d);
  if (mi == inf)
    printf("-1\n");
  else {
    printf("%d\n", mi);
    for (int i = (0), _ed = (((int)(an).size())); i < _ed; i++)
      printf("%d ", an[i]);
  }
  return 0;
}
