#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;

const int N = 1e5 + 7;
struct edge {int u, v, w, id;} e[N];

bool cmp (edge a, edge b) {return a.w < b.w;}

char ch[2];
int n, m, used[N], vis[N], pa[N];

int find (int x) {
	return x == pa[x] ? x : pa[x] = find (pa[x]);
}

int main () {
	scanf ("%d%d", &n, &m);
	for (int i = 1; i <= m; ++i) {
		scanf("%d%d%s", &e[i].u, &e[i].v, ch);
		if (ch[0] == ‘S‘) e[i].w = -1;
		else e[i].w = 1;
		e[i].id = i;
	}
	if (n % 2 == 0) {puts("-1"); return 0;}
	sort (e + 1, e + 1 + m, cmp);
	for (int i = 1; i <= n; ++i) pa[i] = i;
	int tot = 0, val = 0;
	for (int i = 1; i <= m; ++i) {
		int pu = find (e[i].u), pv = find (e[i].v);
		if (pu != pv) {
			pa[pu] = pv;
			++tot;
			val += e[i].w;
			used[e[i].id] = 1;
			if (tot == n - 1) break;
		}
	}
	if (tot < n - 1) {puts("-1"); return 0;}
	if (val > 0) {puts("-1"); return 0;}
	if (val == 0) {
		printf ("%d\n", n - 1);
		for (int i = 1; i <= m; ++i) if(used[i]) printf ("%d ", i);
		return 0;
	}
	val = 0;
	for (int i = 1; i <= n; ++i) pa[i] = i;
	for (int i = 1; i <= m; ++i) 
		if (e[i].w == 1 && used[e[i].id]) vis[e[i].id] = 1, val++, pa[find(e[i].u)] = find(e[i].v);
	for (int i = m; i >= 1; --i) {
		if (val == (n - 1) / 2) break;
		if (used[e[i].id] || e[i].w == -1) continue;
		int pu = find (e[i].u), pv = find (e[i].v);
		if (pu != pv) {val++, pa[pu] = pv, vis[e[i].id] = 1;}
	}
	if (val < (n - 1) / 2) {puts("-1"); return 0;}
	for (int i = 1; i <= m; ++i) {
		if (val == 0) break;
		if (!used[e[i].id] || e[i].w == 1) continue;
		int pu = find (e[i].u), pv = find (e[i].v);
		if (pu != pv) {val--, pa[pu] = pv, vis[e[i].id] = 1;}
	}
	if (val > 0) {puts("-1"); return 0;}
	printf ("%d\n", n - 1);
	for (int i = 1; i <= m; ++i) if (vis[i]) printf ("%d ", i);
	return 0; 
}