#include <bits/stdc++.h>
#define bit(x) (1LL << (x))
#define lowbit(x) (x & (-x))
#define SQU(x) ((x) * (x))
#define ls id << 1
#define rs id << 1 | 1
//#define int long long
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int maxn = 3e5 + 5;
const int inf = 0x3f3f3f3f;
const int mod = 998244353;
const int inv2 = (mod + 1) / 2;
ll qpow(ll x,ll y) {
    ll res = 1;
    while(y) {
        if(y & 1) res = res * x % mod;
        x = x * x % mod;
        y >>= 1;
    }
    return res;
}
void add(int &x,int y) {
    x += y;
    if(x >= mod) x -= mod;
}
const int dx[] = {0,0,1,-1};
const int dy[] = {1,-1,0,0};
int ch[maxn * 30][2],p[maxn * 30],tot;

void insert(int x,int y) {
	int u = 0;
	for(int i = 29;i >= 0;i--) {
		int nxt = ((x >> i) & 1);
		if(!ch[u][nxt]) ch[u][nxt] = ++tot;
		u = ch[u][nxt];
	}
	p[u] = y;
}

pair <int,int> query(int x) {
	int mxu = 0,mnu = 0;
	for(int i = 29;i >= 0;i--) {
		int nxt = ((x >> i) & 1);
		if(ch[mnu][nxt]) mnu = ch[mnu][nxt];
		else mnu = ch[mnu][nxt ^ 1];
		if(ch[mxu][nxt ^ 1]) mxu = ch[mxu][nxt ^ 1];
		else mxu = ch[mxu][nxt];
	}
	return make_pair(min(p[mxu],p[mnu]),max(p[mxu],p[mnu]));
}

void solve() {
	int n,q;cin >> n >> q;
	vector <int> a(n + 1);
	for(int i = 1;i <= n;i++) {
		cin >> a[i];
		insert(a[i],i);
	}
	while(q--) {
		int x,y;cin >> x >> y;
		auto [l,r] = query(x);
		if(l == r) {
			if((x ^ a[1]) == y) cout << "1\n";
			else cout << "-1\n";
			continue;
		}
		if(1LL * ((x ^ a[l]) - y) * ((x ^ a[r]) - y) > 0) {
			cout << "-1\n";
			continue;
		}
		int L = (x ^ a[l]) - y;
		r -= 1;
		while(l < r) {
			int mid = (l + r + 1) >> 1;
			if(1LL * L * ((a[mid] ^ x) - y) > 0) l = mid;
			else r = mid - 1;
		}
		cout << l << '\n';
	}
}
 
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cout << fixed << setprecision(20);
//    freopen("in.txt","r",stdin);
//    freopen("out.txt","w",stdout);
    int T = 1;
//    cin >> T;
    while(T--) {
        solve();
    }
    return 0;
}
/*
*/