#include<bits/stdc++.h>
#define fi first
#define se second
#define m_p make_pair
#define ll long long
#define tc int _TC_; cin >> _TC_; while(_TC_--)
using namespace std;
struct jel{
    int k,v,id;
};
bool comp(jel a, jel b){
    return a.k < b.k;
}
bool comp2(pair<int, int> a, pair<int, int> b){
    return a.fi > b.fi;
}
int main(){
    int m,n;
    cin >> m >> n;
    vector<int> ans;
    vector<jel> je(n);
    for(int i = 0; i < n; i++){
        int a,b;
        cin >> a >> b;
        je[i].id=i+1;
        je[i].k = a;
        je[i].v = b;
    }
    sort(je.begin(), je.end(), comp);
    queue<jel> q;
    for(int i = 0;  i < n; i++){
        q.push(je[i]);
    }
    priority_queue<pair<int, int>> pq;
    int a=0,b=0;
    for(int i = 1; i <= m; i++){
        while(q.front().k == i){
            pq.push(m_p(q.front().v, q.front().id));
            q.pop();
        }
        if(a < i){
            if(pq.empty()){
                ans.clear();
                break;
            }
            a = pq.top().fi;
            ans.push_back(pq.top().se);
            pq.pop();
        }
        if(b < i){
           if(pq.empty()){
                ans.clear();
                break;
            }
            b = pq.top().fi;
            ans.push_back(pq.top().se);
            pq.pop();
        }
        if(min(a, b) < i){
            ans.clear();
            break;
        }
    }
    cout << ans.size() << endl;
    for(int a:ans){
        cout << a << " ";
    }
}