#include <bits/stdc++.h> #define int long long using namespace std; int n,q; int x[1000005]; int a,b; int f(int i){ return (i^a)-b; } signed main(){ freopen("function.in","r",stdin); freopen("function.out","w",stdout); cin>>n>>q; for (int i=1;i<=n;i++){ cin>>x[i]; } while (q--){ cin>>a>>b; int bst=0; for (int i=1;i<n;i++){ if (f(x[i])*f(x[i+1])<=0){ cout<<i<<endl; bst=1; i=n; } } if (bst==0){ cout<<-1<<endl; } } return 0; }