#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 10;
int num[maxn];
int fa[maxn];
int Find(int pos, int e, int x) {
  if (num[fa[pos] - 1] != x && fa[pos] - 1 >= e)
    return fa[pos] - 1;
  else
    return -1;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  int l, r, x;
  cin >> n >> m;
  num[0] = 0;
  for (int i = 1; i <= n; i++) {
    cin >> num[i];
    if (num[i] == num[i - 1])
      fa[i] = fa[i - 1];
    else
      fa[i] = i;
  }
  for (int i = 0; i < m; i++) {
    cin >> l >> r >> x;
    if (num[r] != x)
      cout << r << "\n";
    else
      cout << Find(r, l, x) << "\n";
  }
  return 0;
}
