#include <bits/stdc++.h>
const int Nmax = 100005;
const int Nmic = 105;
const int N = 1005;
using namespace std;
int st, dr, R, L, l, r, x, n, q, i, mij, p;
vector<int> v[10 * Nmax];
int main() {
  scanf("%d%d", &n, &q);
  for (i = 1; i <= n; ++i) {
    scanf("%d", &x);
    v[x].push_back(i);
  }
  for (i = 0; i <= Nmax * 10 - 4; ++i) sort(v[i].begin(), v[i].end());
  for (i = 1; i <= q; ++i) {
    scanf("%d%d%d", &l, &r, &x);
    if (v[x].size() == 0) {
      printf("%d\n", l);
      continue;
    }
    st = 1;
    dr = v[x].size();
    while (st <= dr) {
      mij = (st + dr) / 2;
      if (v[x][mij - 1] < l)
        st = mij + 1;
      else
        dr = mij - 1;
    }
    L = st;
    st = 1;
    dr = v[x].size();
    while (st <= dr) {
      mij = (st + dr) / 2;
      if (v[x][mij - 1] <= r)
        st = mij + 1;
      else
        dr = mij - 1;
    }
    R = dr;
    if (!R || L == v[x].size() + 1) {
      printf("%d\n", l);
      continue;
    }
    if (L - R + 1 == l - r + 1) {
      printf("-1\n");
      continue;
    }
    if (v[x][L - 1] != l) {
      printf("%d\n", l);
      continue;
    }
    st = L;
    dr = R;
    p = l - L;
    while (st <= dr) {
      mij = (st + dr) / 2;
      if (v[x][mij - 1] != p + mij)
        dr = mij - 1;
      else
        st = mij + 1;
    }
    printf("%d\n", v[x][dr - 1] + 1);
  }
  return 0;
}
