#include <bits/stdc++.h>
using namespace std;
template <int POS, class TUPLE>
void deploy(std::ostream &os, const TUPLE &tuple) {}
template <int POS, class TUPLE, class H, class... Ts>
void deploy(std::ostream &os, const TUPLE &t) {
  os << (POS == 0 ? "" : ", ") << get<POS>(t);
  deploy<POS + 1, TUPLE, Ts...>(os, t);
}
template <class T, class U>
std::ostream &operator<<(std::ostream &os, std::pair<T, U> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <class T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v) os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T>
std::ostream &operator<<(std::ostream &os, std::set<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v) os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T, class K>
std::ostream &operator<<(std::ostream &os, std::map<T, K> &make_pair) {
  int remain = make_pair.size();
  os << "{";
  for (auto e : make_pair)
    os << "(" << e.first << " -> " << e.second << ")"
       << (--remain == 0 ? "}" : ", ");
  return os;
}
using ll = long long;
struct NodeMIN {
  int x;
  int id;
  NodeMIN() {
    x = INT_MAX;
    id = 0;
  }
  NodeMIN(int id_, int v) {
    id = id_;
    x = v;
  }
};
template <int NV>
class SegTreeMIN {
  int n;
  vector<NodeMIN> seg_tree;
  inline NodeMIN MAXNODE() { return NodeMIN(0, INT_MAX); }
  inline NodeMIN comp(NodeMIN &a, NodeMIN &b) {
    if (a.x < b.x) {
      return a;
    } else {
      return b;
    }
  }

 public:
  SegTreeMIN() { seg_tree.resize(NV * 2, NodeMIN()); }
  void init(int n_) {
    n = 1;
    while (n < n_) {
      n *= 2;
    }
  }
  inline void update(int k, NodeMIN &a) {
    k += n - 1;
    seg_tree[k] = a;
    while (k > 0) {
      k = (k - 1) / 2;
      seg_tree[k] = comp(seg_tree[k * 2 + 1], seg_tree[k * 2 + 2]);
    }
  }
  inline NodeMIN query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l) {
      return MAXNODE();
    }
    if (a <= l && r <= b) {
      return seg_tree[k];
    }
    NodeMIN vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    NodeMIN vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
    return comp(vl, vr);
  }
  inline NodeMIN query(int a, int b) { return query(a, b, 0, 0, n); }
};
struct NodeMAX {
  int x;
  int id;
  NodeMAX() {
    x = -1;
    id = 0;
  }
  NodeMAX(int id_, int v) {
    id = id_;
    x = v;
  }
};
template <int NV>
class SegTreeMAX {
  int n;
  vector<NodeMAX> seg_tree;
  inline NodeMAX MINNODE() { return NodeMAX(0, -1); }
  inline NodeMAX comp(NodeMAX &a, NodeMAX &b) {
    if (a.x < b.x) {
      return b;
    } else {
      return a;
    }
  }

 public:
  SegTreeMAX() { seg_tree.resize(NV * 2, NodeMAX()); }
  void init(int n_) {
    n = 1;
    while (n < n_) {
      n *= 2;
    }
  }
  inline void update(int k, NodeMAX &a) {
    k += n - 1;
    seg_tree[k] = a;
    while (k > 0) {
      k = (k - 1) / 2;
      seg_tree[k] = comp(seg_tree[k * 2 + 1], seg_tree[k * 2 + 2]);
    }
  }
  inline NodeMAX query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l) {
      return MINNODE();
    }
    if (a <= l && r <= b) {
      return seg_tree[k];
    }
    NodeMAX vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    NodeMAX vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
    return comp(vl, vr);
  }
  inline NodeMAX query(int a, int b) { return query(a, b, 0, 0, n); }
};
SegTreeMAX<400100> STMAX;
SegTreeMIN<400100> STMIN;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  int N, M;
  cin >> N >> M;
  STMAX.init(N + 4);
  STMIN.init(N + 4);
  for (int i = 0; i < (N); i++) {
    int x;
    cin >> x;
    auto nmax = NodeMAX(i, x);
    auto nmin = NodeMIN(i, x);
    STMAX.update(i, nmax);
    STMIN.update(i, nmin);
  }
  for (int i = 0; i < (M); i++) {
    int l, r, x;
    cin >> l >> r >> x;
    l--;
    auto nmax = STMAX.query(l, r);
    auto nmin = STMIN.query(l, r);
    if (nmax.x != x) {
      cout << nmax.id + 1 << "\n";
    } else if (nmin.x != x) {
      cout << nmin.id + 1 << "\n";
    } else {
      cout << -1 << "\n";
    }
  }
  return 0;
}
