#include <bits/stdc++.h>
using namespace std;

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int n,m; cin>>n>>m;
    swap(n,m);
    vector<array<int, 2>> mx(n+1);
    for(int i=1; i<=m; i++)
    {
        int a,b; cin>>a>>b;
        mx[a]=max(mx[a],{b,i});
    }
    for(int i=1; i<=n; i++)
        mx[i]=max(mx[i],mx[i-1]);
    vector<int> ans;
    int curr=1;
    while(curr<n)
    {
        if(mx[curr][0]<=curr) break;
        ans.push_back(mx[curr][1]);
        curr=mx[curr][0];
    }
    if(n==1)
    {
        cout<<"0\n";
        return 0;
    }
    if(curr<n)
    {
        cout<<"-1\n";
        return 0;
    }
    cout<<ans.size()-1<<"\n";
    for(int i:ans)
        cout<<i<<" ";
    cout<<"\n";
}