#include <bits/stdc++.h>   using namespace std;   vector<int> t;   int sz = 0;   const int INF = 2e9;   void build(vector<int> a) {     t.assign(2 * sz + 2, INF);     for (int i = 0; i < sz; i++) {       t[i + sz] = a[i];     }     for (int i = sz - 1; i > 0; i--) {       t[i] = min(t[2 * i], t[2 * i + 1]);     }   }   int get(int v, int tl, int tr, int l, int r) {     if (tl > r || l > tr) {       return INF;     }     if (tl == l && tr == r) {       return t[v];     }     int tm = (tl + tr) / 2;     return min(get(2 * v, tl, tm, l, min(r, tm)),                get(2 * v + 1, tm + 1, tr, max(l, tm + 1), r));   }   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int n;     cin >> n;     sz = 1;     while (sz < 4 * n) {       sz *= 2;     }     vector<int> a(sz);     vector<pair<int, int>> q;     vector<pair<int, int>> qq;     for (int i = 0; i < n; i++) {       int l, r;       cin >> l >> r;       q.emplace_back(l, 0);       qq.emplace_back(l, r);       q.emplace_back(r, 1);       q.emplace_back(l - 1, -1);       q.emplace_back(r + 1, -1);     }     sort(q.begin(), q.end());     int b = 0;     for (int i = 0; i < 4 * n; i++) {       if (q[i].second == 0) {         b++;         int id = lower_bound(q.begin(), q.end(), make_pair(q[i].first, -1)) -                  q.begin();         a[id] = max(a[id], b);       } else {         int id = lower_bound(q.begin(), q.end(), make_pair(q[i].first, -1)) -                  q.begin();         a[id] = max(a[id], b);         if (q[i].second == 1) b--;       }     }     for (int i = 0; i < a.size(); i++) {       if (a[i] == 0) {         a[i] = INF;       }     }     build(a);     for (int i = 0; i < n; i++) {       int minimum = get(           1, 0, sz - 1,           lower_bound(q.begin(), q.end(), make_pair(qq[i].first, -1)) - q.begin(),           lower_bound(q.begin(), q.end(), make_pair(qq[i].second, -1)) -               q.begin());       if (minimum > 1 && minimum != INF) {         cout << i + 1;         return 0;       }     }     cout << -1;     return 0;   }   