#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.12f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<class A,class...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<class A>void PR(A a,ll n){rep(i,n)cout<<(i?" ":"")<<a[i];ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<ll,ll> P;

void Main() {
  ll n,m;
  cin >> n >> m;
  vector<P> v[n];
  rep(i,m) {
    ll x,y;
    cin >> x >> y;
    x--,y--;
    v[x].pb(P(y,i+1));
    v[y].pb(P(x,i+1));
  }
  set<ll> s;
  rep(i,min((int)v[0].size(),2)) {
    rep(j,min((int)v[n-1].size(),2)) {
      if(v[0][i].F!=v[n-1][j].F&&v[0][i].F!=n-1&&v[n-1][j].F!=0) {
        s.in(v[0][i].S);
        s.in(v[n-1][j].S);
        i=j=MAX;
      }
    }
  }
  if(!s.size()) {
    rep(i,v[0].size()) {
      if(v[0][i].F==n-1) {
        s.in(v[0][i].S);
        break;
      }
    }
  }
  pr(s.size());
  tr(it,s) pr(*it);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}