for (int mask = 0; mask < (1 << n); mask++) {
    bool good = true;
    for (int t = 0; t < n; t++) if (((1 << t) & mask) != 0)
        for (int s = 0; s < t; s++) if (((1 << s) & mask) != 0)
            good &= (l[t] >= r[s]) || (r[t] <= l[s]);

    if (good) {
        int cnt = 0;
        for (int t = 0; t < n; t++) cnt += (mask >> t) & 1;
        if (cnt > answ) {
            answ = cnt;
            answ_mask = mask;
        }
    }
}

cout << answ << "\n";
for (int t = 0; t < n; t++) if (((1 << t) & answ_mask) != 0) cout << l[t] << " " << r[t] << "\n";