#include <bits/stdc++.h>

using namespace std;


int main()
{
    int n, m;
    cin >> n >> m;
    vector<pair<int, pair<int, int> > > vasut;
    for (int i=0; i<n; i++) {
        int x, y;
        cin >> x >> y;
        x--;
        y--;
        if (x<y) {
            swap(x, y);
        }
        vasut.push_back({x, {y, i+1}});
    }
    sort(vasut.begin(), vasut.end());
    reverse(vasut.begin(), vasut.end());
    int epp=0;
    vector<int> utvonal;
    int valtozas=1;
    while (valtozas!=epp) {
        valtozas=epp;
        for (int j=0; j<m; j++) {
            if (vasut[j].second.first<=epp && vasut[j].first>epp) {
                epp=vasut[j].first;
                utvonal.push_back(vasut[j].second.second);
                break;
            }
        }
    }
    if (epp==m-1) {
        cout << utvonal.size()-1 << "\n";
        for (int sz : utvonal) {
            cout << sz << " ";
        }
    }
    else {
        cout << "-1";
    }


    return 0;
}