//                            _ooOoo_
//                           o8888888o
//                           88" . "88
//                           (| -_- |)
//                            O\ = /O
//                        ____/`---'\____
//                      .   ' \\| |// `.
//                       / \\||| : |||// \
//                     / _||||| -:- |||||- \
//                       | | \\\ - /// | |
//                     | \_| ''\---/'' | |
//                      \ .-\__ `-` ___/-. /
//                   ___`. .' /--.--\ `. . __
//                ."" '< `.___\_<|>_/___.' >'"".
//               | | : `- \`.;`\ _ /`;.`/ - ` : | |
//                 \ \ `-. \_ __\ /__ _/ .-` / /
//         ======`-.____`-.___\_____/___.-`____.-'======
//                            `=---='
//
//         .............................................
//    佛曰:     佛祖镇楼                  BUG辟易

#include <bits/stdc++.h>
#include <iostream>
#include <cstring>
#include <vector>
#include <queue>
#include <deque>
#include <utility>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include<cmath>
#include<string>
#include<cstring>
#define int long long
#define endl '\n'
using namespace std;

const int N=1e7+10;
const int INF=9223372036854775807;
const int inf=0x3f3f3f3f;
typedef pair<int,int> PII;
typedef pair<double,int> PDI;
typedef pair<int,double> PID;

int tr[N][2];
int tag[N];

int cnt=1;

void build (int x,int pos) {
    int loc = 1;
    for (int i = 31; i >= 0; i--) {
        int flag = (x >> i) & 1;
        if (tr[loc][flag] == 0) {
            cnt++;
            tr[loc][flag] = cnt;
            tag[cnt] = inf;
        }
        loc = tr[loc][flag];
        tag[loc] = min(tag[loc], pos);
    }
}

int find1(int x,int y) {
    int loc = 1;
    for (int i = 31; i >= 0; i--) {
        int x1 = (x >> i) & 1;
        int y1 = (y >> i) & 1;
        if (tr[loc][x1 ^ y1] == 0) {
            cnt++;
            tr[loc][x1 ^ y1] = cnt;
            tag[cnt] = inf;
        }
        loc = tr[loc][x1 ^ y1];
    }
    if (tag[loc] != inf && tag[loc] > 1) return tag[loc] - 1;
    else return tag[loc];
}

int find2(int x,int y) {
    int loc = 1;
    int l = inf, r = inf;
    for (int i = 31; i >= 0; i--) {
        int x1 = (x >> i) & 1;
        int y1 = (y >> i) & 1;
        if (y1 == 1) {
            l = min(l, tag[tr[loc][x1]]);
        } else {
            r = min(r, tag[tr[loc][x1 ^ 1]]);
        }
        loc = tr[loc][x1 ^ y1];
    }
    l = min(l, tag[loc]);
    r = min(r, tag[loc]);
    if (l == inf || r == inf) return -1;
    else return max(l, r) - 1;
}

void solve() {
    int n, q;
    cin >> n >> q;
    tag[0] = inf;
    tag[1] = inf;
    int x;
    for (int i = 1; i <= n; i++) {
        cin >> x;
        build(x, i);
    }
    int a, b;
    for (int i = 1; i <= q; i++) {
        cin >> a >> b;
        int f = find1(a, b);//判断是不是 f(x)*f(x+1) = 0 的情况
        if (f != inf) cout << f << endl;
        else cout << find2(a, b) << endl;
    }
    return;
}

signed main() {
    std::ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t=1;
    //cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}