#include<bits/stdc++.h>
#define ll int
using namespace std;
const ll _=1e6+5,N=_<<5;
struct o{ll x,y;bool operator<(const o &t)const{return x<t.x;}};
ll n,q,x,y,z,l,r,a[_],c[N],rt,T,L[N],R[N],i;set<o>b;
void upd(ll x){
	ll *t=&rt,i;
	for(i=30;i--;){
		if(!*t)*t=++T;c[*t]++;
		t=&(((x>>i)&1)?R:L)[*t];
	}
	if(!*t)*t=++T;c[*t]++;
}
ll p(ll x){return b.lower_bound({x,0})->y;}
ll que(ll x,ll y,bool f){
	ll t=rt,k=0,i;
	for(i=30;i--;){
		if(!t||!c[t])return -1;
		if(((x^y)>>i)&1){
			if((((y>>i)&1)^f)&&c[L[t]])return p(k);
			t=R[t];k|=(1<<i);
		}
		else{
			if((((y>>i)&1)^f)&&c[R[t]])return p(k|(1<<i));
			t=L[t];
		}
	}
	return -1;
}
ll P(){
	auto it=b.lower_bound({x^y,0});
	if((it->x)==(x^y))return ((it->y)-1)?:1;
	bool u=((a[1]^x)<y);
	l=1;r=que(x,y,u);if(r<0)return -1;
	while(l+1<r){z=(l+r)>>1;if(((a[z]^x)<y)==u)l=z;else r=z;}
	return l;
}
int main(){
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>n>>q;
	for(i=1;i<=n;i++)cin>>a[i],b.insert({a[i],i}),upd(a[i]);
	while(q--){
		cin>>x>>y;
		cout<<P()<<'\n';
	}
}