#include<bits/stdc++.h>
#define endl        '\n'
#define F           first
#define S           second
#define pb          push_back
#define yes         cout<<"YES\n"
#define no          cout<<"NO\n"
#define all(x)      x.begin(),x.end()
#define allr(x)     x.rbegin(),x.rend()
#define error1(x)   cerr<<#x<<" = "<<(x)<<endl
#define error2(a,b) cerr<<"("<<#a<<", "<<#b<<") = ("<<(a)<<", "<<(b)<<")\n";
#define coutall(v)  for(auto &it: v) cout << it << " "; cout << endl;
using namespace std;
using ll = long long;
using ld = long double;

const int N = 3e5 + 3;

struct Merge_Sort_Tree {
    vector<set<pair<int, int>>> t;

    Merge_Sort_Tree() {
        t.resize(4 * N, {});
    }

    void build(int node, int st, int en, vector<int> &arr) { //=> O(N log N)
        t[node].clear();
        if (st == en) {
            t[node].insert({1, arr[st]});
            return;
        }
        int mid = (st + en) >> 1;
        build(node << 1, st, mid, arr); // divide left side
        build(node << 1 | 1, mid + 1, en, arr); // divide right side

        // Merging left and right portion
        auto &Cur = t[node];
        auto &Left = t[node << 1];
        auto &Right = t[node << 1 | 1];
        
        map<int, int> mp;
        for(auto &i: Left) mp[i.S] += i.F;
        for(auto &i: Right) mp[i.S] += i.F;
        for(auto &i: mp) Cur.insert({i.S, i.F});
    }
    set<pair<int, int>> em;
    set<pair<int, int>> query(int node, int st, int en, int l, int r) { //=> O(log N * log N)
        // assert(l <= r); // <==
        if (st > r || en < l) { // No overlapping and out of range
            return em; // <== careful 
        }
        if (l <= st && en <= r) { // Complete overlapped (l-r in range)
            return t[node];
        }
        // Partial overlapping
        int mid = (st + en) >> 1;
        auto Left = query(node << 1, st, mid, l, r);
        auto Right = query(node << 1 | 1, mid + 1, en, l, r);
        map<int, int> mp;
        set<pair<int, int>> Cur;
        for(auto &i: Left) mp[i.S] += i.F;
        for(auto &i: Right) mp[i.S] += i.F;
        for(auto &i: mp) Cur.insert({i.S, i.F});
        return Cur;
    }
} st1;

void solve() {
    int n, q;
    cin >> n >> q;
    vector<int> v(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }
    st1.build(1, 0 , n - 1, v);
    int l, r, k;
    while(q--) {
        cin >> l >> r; --l, --r;
        k = (r - l + 1) / 3;
        auto st = st1.query(1, 0, n - 1, l, r);
        if(st.rbegin()->F > k) {
            auto it = st.lower_bound(make_pair(k + 1, -1));
            int ans = INT_MAX;
            while(it != st.end()) {
                ans = min(ans, it->S);
                ++it;
            }
            cout << ans << endl;
        }
        else cout << -1 << endl;
    }
    return;
}

signed main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int tc = 1;
    // cin >> tc;
    for (int t = 1; t <= tc; t++) {
        // cout << "Case " << t << ": ";
        solve();
    }
    return 0;
}