#include <bits/stdc++.h>
using namespace std;
const double PI = 2.0 * acos(0.0);
const double EX = 2.7182818284;
const int MOD = 1e9 + 7;
const int oo = 2e9 + 1e8;
long long gcd(long long x, long long y) { return !y ? x : gcd(y, x % y); }
const int mx = 1e6 + 10;
int n, m, l, r, x, ans;
pair<int, int> idx[mx];
bool vis[mx];
int main() {
  scanf("%d%d", &n, &m);
  vector<int> in(n + 1), dp(n + 1);
  for (int i = 1; i < n + 1; i++) {
    scanf("%d", &in[i]);
    if (in[i] != in[i - 1]) dp[i] = 1;
  }
  in[0] = -1;
  idx[1] = make_pair(0, 1);
  for (int i = 2; i < n + 1; i++) {
    if (dp[i])
      idx[i] = make_pair(i - 1, i);
    else
      idx[i] = make_pair(idx[i - 1].first, i);
  }
  while (m-- && scanf("%d%d%d", &l, &r, &x)) {
    if (l == r) {
      if (in[idx[r].second] != x)
        ans = idx[r].second;
      else
        ans = -1;
    } else {
      if (in[idx[r].second] != x)
        ans = idx[r].second;
      else if (idx[r].first >= l && in[idx[r].first] != x)
        ans = idx[r].first;
      else
        ans = -1;
    }
    printf("%d\n", ans);
  }
  return 0;
}
