5

#include "bits/stdc++.h"

#define endl "\n"
using namespace std;
using pii = pair<int, int>;

void solve() {
  int n;
  cin >> n;
  vector<int> a(n);
  vector<int> b(n);
  for (int& v: a)
    cin >> v;
  for (int& v: b)
    cin >> v;
  queue<pii> q;
  q.emplace(0, 0);
  set<int> used;
  for (int i = 1; i <= n; ++i)
    used.insert(i);
  vector<int> ans(n + 1, -1);
  ans[0] = 0;
  while(q.size()) {
    auto [num, cur] = q.front();
    q.pop();
    if (cur == n) {
      break;
    }
    for (auto it = used.lower_bound(cur); it != used.end() && *it <= cur + a[n - cur - 1]; it = used.erase(it)) {
      int new_height = *it;
      if (ans[new_height - b[n - new_height - 1]] == -1) {
        ans[new_height - b[n - new_height - 1]] = num + 1;
        q.emplace(num + 1, new_height - b[n - new_height - 1]);
      }
    }
  }
  cout << ans[n] << endl;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int tests = 1;
  //cin >> tests;
  while(tests--) {
    //auto start = chrono::high_resolution_clock::now();
      solve();
    // auto end = chrono::high_resolution_clock::now();
    // cout << endl << (chrono::duration_cast<chrono::duration<double>>(end - start)).count();
  }
  return 0;
}