#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define all(arr) (arr).begin(), (arr).end()
#define ll long long
#define ld long double
#define pb push_back
#define sz(x) (int)(x).size()
#define fi first
#define se second
#define endl '\n'

signed main(){
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  // cout.precision(20);
  int n;
  cin >> n;
  vector<int> r(n);
  for (int i = 0; i < n; i++){
    int x, y;
    cin >> x >> y;
    y--;
    r[i] = y;
  }
  int q, foo;
  cin >> q >> foo;
  int prevrb = -1, rb = r[0], ans = 1;
  while (rb < n - 1){
    int newrb = rb;
    for (int i = prevrb + 1; i <= rb; i++){
      newrb = max(newrb, r[i]);
    }
    if (newrb == rb){
      cout << -1 << endl;
      return 0;
    }
    prevrb = rb, rb = newrb, ans++;
  }
  cout << ans << endl;
}