#include <bits/stdc++.h> #define int long long using namespace std; int n,q; int x[1000005],a,b; int f(int x){ return (x^a)-b; } signed main(){ cin>>n>>q; for (int i=1;i<=n;i++)cin>>x[i]; while (q--){ cin>>a>>b; bool bt=0; for (int i=1;i<n;i++){ if (f(i)*f(i+1)<=0){ cout<<i<<endl; bt=1; i=n; } } if (bt==0){ cout<<-1<<endl; } } return 0; }