#include <bits/stdc++.h>

using namespace std;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n) for(int i = 0; i < (int)(n); ++i)
#define rep2(i, n) for(int i = 0; i < (int)(n); ++i)
#define rep3(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep4(i, a, b, c) for(int i = (a); i < (int)(b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)

#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i)
#define ALL(a) (a).begin(), (a).end()
#define Sort(a) (sort((a).begin(), (a).end()))
#define RSort(a) (sort((a).rbegin(), (a).rend()))
#define UNIQUE(a) (a.erase(unique((a).begin(), (a).end()), (a).end()))

typedef long long int ll;
typedef unsigned long long ul;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<char> vc;
typedef vector<string> vst;
typedef vector<double> vd;
typedef vector<long double> vld;
typedef pair<long long, long long> P;

template<class T> long long sum(const T& a){ return accumulate(a.begin(), a.end(), 0LL); }
template<class T> auto min(const T& a){ return *min_element(a.begin(), a.end()); }
template<class T> auto max(const T& a){ return *max_element(a.begin(), a.end()); }

const long long MINF = 0x7fffffffffff;
const long long INF = 0x1fffffffffffffff;
const long long MOD = 998244353;
const long double EPS = 1e-9;
const long double PI = acos(-1);
 
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p){ is >> p.first >> p.second; return is; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){ os << "(" << p.first << ", " << p.second << ")"; return os; }
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for(T &in : v) is >> in; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v){ for(int i = 0; i < (int) v.size(); ++i){ os << v[i] << (i + 1 != (int) v.size() ? " " : ""); } return os; }
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp){ for(auto &[key, val] : mp){ os << key << ":" << val << " "; } return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, queue<T> q){ while(q.size()){ os << q.front() << " "; q.pop(); } return os; }
template <typename T> ostream &operator<<(ostream &os, deque<T> q){ while(q.size()){ os << q.front() << " "; q.pop_front(); } return os; }
template <typename T> ostream &operator<<(ostream &os, stack<T> st){ while(st.size()){ os << st.top() << " "; st.pop(); } return os; }
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq){ while(pq.size()){ os << pq.top() << " "; pq.pop(); } return os; }

template<class T, class U> inline T vin(T& vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; }
template<class T> inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; }
template<class... T> void in(T&... a){ (cin >> ... >> a); }
void out(){ cout << '\n'; }
template<class T, class... Ts> void out(const T& a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T, class U> void inGraph(vector<vector<T>>& G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; ++i){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } }

void input(){
}

struct GabowEdmonds {

  struct edge {
    int to, idx;
  };

  vector< vector< edge > > g;
  vector< pair< int, int > > edges;
  vector< int > mate, label, first;
  queue< int > que;

  GabowEdmonds(int n) : g(n + 1), mate(n + 1), label(n + 1, -1), first(n + 1) {}

  void add_edge(int u, int v) {
    ++u, ++v;
    g[u].push_back((edge) {v, (int) (edges.size() + g.size())});
    g[v].push_back((edge) {u, (int) (edges.size() + g.size())});
    edges.emplace_back(u, v);
  }

  int find(int x) {
    if(label[first[x]] < 0) return first[x];
    first[x] = find(first[x]);
    return first[x];
  }

  void rematch(int v, int w) {
    int t = mate[v];
    mate[v] = w;
    if(mate[t] != v) return;
    if(label[v] < g.size()) {
      mate[t] = label[v];
      rematch(label[v], t);
    } else {
      int x = edges[label[v] - g.size()].first;
      int y = edges[label[v] - g.size()].second;
      rematch(x, y);
      rematch(y, x);
    }
  }

  void assign_label(int x, int y, int num) {
    int r = find(x);
    int s = find(y);
    int join = 0;
    if(r == s) return;
    label[r] = -num;
    label[s] = -num;
    while(true) {
      if(s != 0) swap(r, s);
      r = find(label[mate[r]]);
      if(label[r] == -num) {
        join = r;
        break;
      }
      label[r] = -num;
    }
    int v = first[x];
    while(v != join) {
      que.push(v);
      label[v] = num;
      first[v] = join;
      v = first[label[mate[v]]];
    }
    v = first[y];
    while(v != join) {
      que.push(v);
      label[v] = num;
      first[v] = join;
      v = first[label[mate[v]]];
    }
  }

  bool augment_check(int u) {
    que = queue< int >();
    first[u] = 0;
    label[u] = 0;
    que.push(u);
    while(!que.empty()) {
      int x = que.front();
      que.pop();
      for(auto e : g[x]) {
        int y = e.to;
        if(mate[y] == 0 && y != u) {
          mate[y] = x;
          rematch(x, y);
          return true;
        } else if(label[y] >= 0) {
          assign_label(x, y, e.idx);
        } else if(label[mate[y]] < 0) {
          label[mate[y]] = x;
          first[mate[y]] = y;
          que.push(mate[y]);
        }
      }
    }
    return false;
  }

  vector< pair< int, int > > max_matching() {
    for(int i = 1; i < g.size(); i++) {
      if(mate[i] != 0) continue;
      if(augment_check(i)) label.assign(g.size(), -1);
    }
    vector< pair< int, int > > ret;
    for(int i = 1; i < g.size(); i++) {
      if(i < mate[i]) ret.emplace_back(i - 1, mate[i] - 1);
    }
    return ret;
  }
};

void solve(){
    ll n, m; in(n, m);
    assert(n <= 2000);
    GabowEdmonds flow(n);
    map<P, ll> mp;
    rep(i, m){
        ll a, b;
        in(a, b);  a--, b--;
        flow.add_edge(a, b);
        mp[{a, b}] = i, mp[{b, a}] = i;
    }
    auto ret = flow.max_matching();
    cout << ret.size() << endl;
    for(auto &p : ret) out(mp[p] + 1);
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
    
    input();
    solve();
}