#include <bits/stdc++.h>
using namespace std;
int a[200010];
struct seg {
  int val, idx;
} tree1[600010], tree2[600010];
void build(int node, int s, int e) {
  if (s > e) return;
  if (s == e) {
    tree1[node].val = a[s];
    tree1[node].idx = s;
    tree2[node].val = a[s];
    tree2[node].idx = s;
    return;
  }
  int mid = (s + e) / 2;
  build(2 * node, s, mid);
  build(2 * node + 1, mid + 1, e);
  if (tree1[2 * node].val > tree1[2 * node + 1].val)
    tree1[node].idx = tree1[2 * node + 1].idx;
  else
    tree1[node].idx = tree1[2 * node].idx;
  if (tree2[2 * node].val > tree2[2 * node + 1].val)
    tree2[node].idx = tree2[2 * node].idx;
  else
    tree2[node].idx = tree2[2 * node + 1].idx;
  tree1[node].val = min(tree1[2 * node].val, tree1[2 * node + 1].val);
  tree2[node].val = max(tree2[2 * node].val, tree2[2 * node + 1].val);
}
seg query1(int node, int s, int end, int l, int r) {
  if (s > end || s > r || end < l) {
    seg temp;
    temp.val = 1000000000;
    temp.idx = -1;
    return temp;
  }
  if (s >= l && end <= r) return tree1[node];
  seg res1 = query1(2 * node, s, (s + end) / 2, l, r);
  seg res2 = query1(2 * node + 1, (s + end) / 2 + 1, end, l, r);
  seg res;
  if (res1.val < res2.val) {
    res.val = res1.val;
    res.idx = res1.idx;
  } else {
    res.val = res2.val;
    res.idx = res2.idx;
  }
  return res;
}
seg query2(int node, int s, int end, int l, int r) {
  if (s > end || s > r || end < l) {
    seg temp;
    temp.val = -1000000000;
    temp.idx = -1;
    return temp;
  }
  if (s >= l && end <= r) return tree2[node];
  seg res1 = query2(2 * node, s, (s + end) / 2, l, r);
  seg res2 = query2(2 * node + 1, (s + end) / 2 + 1, end, l, r);
  seg res;
  if (res1.val > res2.val) {
    res.val = res1.val;
    res.idx = res1.idx;
  } else {
    res.val = res2.val;
    res.idx = res2.idx;
  }
  return res;
}
int main() {
  int n;
  cin >> n;
  int q;
  cin >> q;
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  build(1, 0, n - 1);
  while (q--) {
    int l, r, x;
    scanf("%d %d %d", &l, &r, &x);
    l--;
    r--;
    seg mx = query1(1, 0, n - 1, l, r);
    seg mi = query2(1, 0, n - 1, l, r);
    if (mx.val == x && mi.val == x) {
      printf("-1\n");
    } else if (mx.val == x) {
      printf("%d\n", mi.idx + 1);
    } else
      printf("%d\n", mx.idx + 1);
  }
  return 0;
}
