#include <bits/stdc++.h>
using namespace std;
int n, m;
vector<int> adj0[100010], adj1[100010], idx[100010];
vector<pair<pair<int, int>, int> > edge0, edge1, fedge;
bool vis[100010];
int x, y, z;
struct node {
  int p, l;
} st[100010];
void add(int a, int p) {
  st[a].p = p;
  st[p].l = 1;
}
void mrge(int x, int y) {
  while (st[x].p != x) {
    x = st[x].p;
  }
  while (st[y].p != y) {
    y = st[y].p;
  }
  if (x == y) return;
  if (st[x].l < st[y].l)
    swap(x, y);
  else if (st[x].l == st[y].l)
    st[x].l++;
  st[y].p = x;
}
int chk(int x, int y) {
  while (st[x].p != x) {
    x = st[x].p;
  }
  while (st[y].p != y) {
    y = st[y].p;
  }
  if (x == y)
    return 1;
  else
    return 0;
}
int get_cnt() {
  long long tmp, ret = (n - 1);
  ret *= y;
  ret = z - ret;
  tmp = x - y;
  if ((ret % tmp) != 0) {
    return -1;
  } else {
    return ret / tmp;
  }
}
int get_cnt1() {
  if ((n % 2) == 0)
    return -1;
  else
    return (n - 1) / 2;
}
void dfs(int a) {
  if (vis[a] == true) return;
  vis[a] = true;
  for (int i = 0; i < adj0[a].size(); i++) {
    dfs(adj0[a][i]);
  }
}
void solve() {
  int a, b, c;
  char ch;
  scanf("%d", &n);
  ;
  scanf("%d", &m);
  ;
  for (int i = 0; i < m; i++) {
    scanf("%d", &a);
    ;
    scanf("%d", &b);
    ;
    cin >> ch;
    if (ch == 'S') {
      adj0[a].push_back(b);
      adj0[b].push_back(a);
      idx[a].push_back(i + 1);
      idx[b].push_back(i + 1);
      edge0.push_back(make_pair(make_pair(a, b), i + 1));
    } else {
      adj1[a].push_back(b);
      adj1[b].push_back(a);
      idx[a].push_back(i + 1);
      idx[b].push_back(i + 1);
      edge1.push_back(make_pair(make_pair(a, b), i + 1));
    }
  }
  if (n == 1) {
    printf("0\n");
    return;
  }
  int cnt1 = get_cnt1();
  if (cnt1 == -1) {
    printf("-1\n");
    return;
  }
  int cnt = 0, cnt2 = n - cnt1 - 1;
  for (int i = 1; i <= n; i++) {
    if (vis[i] == 0) {
      cnt++;
      dfs(i);
    }
  }
  if (cnt - 1 > cnt2) {
    printf("-1\n");
    return;
  }
  for (int i = 1; i <= n; i++) {
    add(i, i);
  }
  for (int i = 0; i < edge0.size(); i++) {
    mrge(edge0[i].first.first, edge0[i].first.second);
  }
  for (int i = 0; i < edge1.size(); i++) {
    if (chk(edge1[i].first.first, edge1[i].first.second) == 0) {
      fedge.push_back(edge1[i]);
      mrge(edge1[i].first.first, edge1[i].first.second);
    }
  }
  for (int i = 1; i <= n; i++) {
    st[i].p = i;
    st[i].l = 0;
  }
  for (int i = 1; i <= n; i++) {
    add(i, i);
  }
  for (int i = 0; i < fedge.size(); i++) {
    mrge(fedge[i].first.first, fedge[i].first.second);
    cnt2--;
  }
  for (int i = 0; i < edge1.size(); i++) {
    if (chk(edge1[i].first.first, edge1[i].first.second) == 0) {
      fedge.push_back(edge1[i]);
      mrge(edge1[i].first.first, edge1[i].first.second);
      cnt2--;
      if (cnt2 == 0) break;
    }
  }
  if (cnt2 > 0) {
    printf("-1\n");
    return;
  }
  for (int i = 0; i < edge0.size(); i++) {
    if (chk(edge0[i].first.first, edge0[i].first.second) == 0) {
      fedge.push_back(edge0[i]);
      mrge(edge0[i].first.first, edge0[i].first.second);
      cnt1--;
      if (cnt1 == 0) break;
    }
  }
  if (cnt1 > 0) {
    printf("-1\n");
    return;
  }
  cout << fedge.size() << endl;
  for (int i = 0; i < fedge.size(); i++) {
    printf("%d ", fedge[i].second);
  }
  printf("\n");
}
int main() {
  int t = 1;
  for (int i = 1; i <= t; i++) {
    solve();
  }
}
