#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
//#include <intrin.h>

#define fore(i,a,b) for(int i = a; i < (b); i++)
#define fr(i,a,b) for(int i = a - 1; i >= b; i--)
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define N 300005
#define inf 2000000000
#define EPS 1e-6
#define MOD (ll)1e15
#define __builtin_popcount(x) __popcnt(x)

using namespace std;

typedef long long ll;
typedef pair<int, int> pr;
typedef pair<int, pair<int, int>> tup;

struct SegTree {
	vector<pair<pair<int, int>, pair<int, int>>> tree;

	void resize(int n)
	{
		tree.resize(4 * n);
	}

	void build(int l, int r, int v, vector<int> &a)
	{
		if (l == r)
			tree[v] = { {a[l], l}, {a[l], l} };
		else
		{
			int m = (r + l) / 2;

			build(l, m, 2 * v, a);
			build(m + 1, r, 2 * v + 1, a);

			tree[v].first = min(tree[2 * v].first, tree[2 * v + 1].first);
			tree[v].second = max(tree[2 * v].second, tree[2 * v + 1].second);
		}
	}

	pair<pair<int, int>,pair<int,int>> query(int ql, int qr, int l, int r, int v)
	{
		if (ql > qr)
			return { {inf, -1}, {-inf, -1} };
		else if (ql == l && qr == r)
			return tree[v];
		else
		{
			int m = (r + l) / 2;

			pair<pair<int, int>, pair<int, int>> res1 = query(ql, min(qr, m), l, m, 2 * v);
			pair<pair<int, int>, pair<int, int>> res2 = query(max(m + 1, ql), qr, m + 1, r, 2 * v + 1);

			return { min(res1.first, res2.first), max(res1.second, res2.second) };
		}
	}
};

inline void solve()
{
	int n, m;
	cin >> n >> m;
	vector<int> v(n);
	fore(i, 0, n)
		cin >> v[i];

	SegTree t;
	t.resize(n);
	t.build(0, n - 1, 1, v);
	fore(i, 0, m)
	{
		int l, r, q;
		cin >> l >> r >> q;

		pair<pair<int, int>, pair<int, int>> res = t.query(l - 1, r - 1, 0, n - 1, 1);

		if (res.first.first == q && res.second.first == q)
			cout << -1;
		else if (res.first.first != q)
			cout << res.first.second + 1;
		else
			cout << res.second.second + 1;

		cout << '\n';
	}
}

int main()
{
	fast;
#if defined(_DEBUG)
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	int q = 1;
	//cin >> q;
	while (q--)
	{
		solve();
		cout << '\n';
	}
}