#include <bits/stdc++.h>
using namespace std;
int setBit(int n, int pos) { return n = n | (1 << pos); }
int resetBit(int n, int pos) { return n = n & ~(1 << pos); }
bool checkBit(int n, int pos) { return (bool)(n & (1 << pos)); }
int n, m, A[1000000 + 10];
vector<int> pos[1000000 + 10];
int ok(int st, int ed, int x) {
  if (A[st] != x)
    return 1;
  else if (A[ed] != x)
    return 1;
  auto L = lower_bound(pos[x].begin(), pos[x].end(), st);
  auto R = lower_bound(pos[x].begin(), pos[x].end(), ed);
  int have = (R - L) + 1;
  if (have == (ed - st + 1)) {
    return -1;
  } else
    return 1;
}
int solve(int st, int ed, int x) {
  if (ok(st, ed, x) == -1) return -1;
  while (st < ed) {
    int mid = (st + ed) / 2;
    if (ok(st, mid, x) != -1)
      ed = mid;
    else
      st = mid + 1;
  }
  return st;
}
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &A[i]);
    pos[A[i]].push_back(i);
  }
  int st, ed, x;
  while (m--) {
    scanf("%d %d %d", &st, &ed, &x);
    printf("%d\n", solve(st, ed, x));
  }
  return 0;
}
