#include <bits/stdc++.h>
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define rep(i,N) for(long long i = 0; i < (long long)(N); i++)
#define repr(i,N) for(long long i = (long long)(N) - 1; i >= 0; i--)
#define rep1(i,N) for(long long i = 1; i <= (long long)(N) ; i++)
#define repr1(i,N) for(long long i = (N) ; (long long)(i) > 0 ; i--)
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) long long __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
using namespace std; void solve();
using ll = long long; template<class T = ll> using V = vector<T>;
using vi = V<int>; using vl = V<>; using vvi = V< V<int> >;
constexpr int inf = 1001001001; constexpr ll infLL = (1LL << 61) - 1;
struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); rep(i,s) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);} while(0)
  #define trcc(v) do { cerr << "name : " << #v << "\n"; int cnt = 0; each(x , v){cerr << (cnt++) << " : "; trc(x); } } while(0)
#else
  #define trc(...)
  #define trca(...)
  #define trcc(...)
  int main(){solve();}
#endif

#define inc(...) char __VA_ARGS__; in(__VA_ARGS__)
#define in2(s,t)   rep(i,sz(s)){in(s[i] , t[i]);}
#define in3(s,t,u) rep(i,sz(s)){in(s[i] , t[i] , u[i]);}
using vd = V<double>; using vs = V<string>; using vvl = V< V<> >;
template<typename T,typename U>ll ceil(T a,U b){return (a + b - 1) / b;}

using P = pair<ll,ll>; using vp = V<P>;
constexpr int MOD = /**/ 1000000007; //*/ 998244353;
//////////////////

// Union-Find木
// 初期化 UF(N); Nは要素数
// 結合 unite(x,y); 同じ集合か判定 same(x,y);
// 集合の数 count
struct UF{
  vector<int> par,sizes;
  int cnt;
  UF(int N) : par(N),sizes(N, 1),cnt(N){ for(int i=0; i<N; i++) par[i]=i; }

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

  bool same(int x,int y){ return find(x) == find(y); }

  int size(int x){ return sizes[find(x)]; }

  void unite(int x, int y){
    x = find(x); y = find(y);
    if(x == y) return;
    if(sizes[x] < sizes[y]) swap(x,y);
    par[y] = x;
    sizes[x] += sizes[y];
    cnt--;
  }
  
  int count() const{return cnt;}
};

void solve(){
  ini(N , M);
  vp A(N) , B(M); in(A , B);
  sort(all(A));
  A.eb(infLL , 0);
  vi D(N + 1);
  D[0] = A[0].second;
  rep1(i , N) D[i] = A[i - 1].second ^ A[i].second;
  trc(A);
  trc(D);

  map<pair<int,int>,int> m;
  vvi g(N + 1);

  rep(i , M){
    int l = B[i].first , r = B[i].second;
    int s = upper_bound(all(A) , P(l , -1)) - begin(A);
    int t = upper_bound(all(A) , P(r , inf)) - begin(A);
    if(s == t) continue;
    m[minmax(s , t)] = i;
    g[s].pb(t); g[t].pb(s);
  }

  trcc(m);
  vi visited(N + 1);
  vi ans(M);
  trc(D);
  auto dfs = [&](auto rec,int cur,int par) -> void{
    visited[cur] = 1;
    trc(cur , par);
    each(dst , g[cur]){
      if(dst == par) continue;
      if(visited[dst]) continue;
      if(D[cur] == 1){
        ans[ m[minmax(cur , dst)] ] ^= 1; 
        D[cur] ^= 1; D[dst] ^= 1;
      }
      rec(rec , dst , cur);
      if(D[dst] == 1){
        ans[ m[minmax(cur , dst)] ] ^= 1;
        D[cur] ^= 1; D[dst] ^= 1;
      }
    }
  };

  // dfs木でオイラーツアーして奇偶が一致するものを全部押す
  rep(i , N + 1){
    if(D[i] == 0) continue;
    if(visited[i] == 1 && D[i] == 1) die(-1);
    if(visited[i] == 0) dfs(dfs , i , -1);
  }

  trc(ans);
  trc(D);
  each(x , D) if(x != 0) die(-1);
  vi bns; 
  rep(i , M) if(ans[i] == 1) bns.pb(i + 1);
  out(sz(bns));
  out(bns); 


  

}

Measured memory_bytes: 37348