Segment Tree

/*If you want something you've never had, you have  to do something you never did.*/

#include<bits/stdc++.h>
using namespace std;


#define pb push_back
#define ll long long
#define pii pair<ll,ll>
#define pll pair<ll,ll>
#define M 100007
#define INF 1e9
#define INFL 1e18
#define PI acos(-1)
#define mp make_pair
#define fast_in_out ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//const ll fx[]= {+1,-1,+0,+0};
//const ll fy[]= {+0,+0,+1,-1};
//const ll fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const ll fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const ll fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const ll fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move

ll tree[4*150000];
ll arr[150100];
ll n,m;


ll mypow(ll x)
{
    ll ans=1;
    while(x!=0)
    {
        ans=ans*2;
        x--;
    }
    return ans;
}
void init(ll node,ll b,ll e,ll flag)
{
    if(b==e)
    {
        tree[node]=arr[b];
        return;
    }
    ll left=node*2;
    ll right=node*2+1;
    ll mid=(b+e)/2;
    init(left,b,mid,(flag+1)%2);
    init(right,mid+1,e,(flag+1)%2);
    if(flag==0)
    {
        tree[node]=(tree[left] | tree[right]);
//        cout<<node<<" "<<tree[node]<<" "<<flag<<endl;
    }
    else
    {
        tree[node]=(tree[left] ^ tree[right]);
//        cout<<node<<" "<<tree[node]<<" "<<flag<<endl;
    }
}

void update(ll node,ll b,ll e,ll i,ll newvalue,ll flag)
{
    if(i>e || i<b)
        return;
    if(b==e)
    {
        tree[node]=newvalue;
        return;
    }
    ll left=node*2;
    ll right=node*2+1;
    ll mid=(b+e)/2;
    update(left,b,mid,i,newvalue,(flag+1)%2);
    update(right,mid+1,e,i,newvalue,(flag+1)%2);
    if(flag==0)
    {
         tree[node]=(tree[left] | tree[right]);
    }
    else
    {
         tree[node]=(tree[left] ^ tree[right]);
    }
}

int main()
{
    fast_in_out;
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    ll x;
    cin>>x>>m;
    n=mypow(x);
    for(ll i=1;i<=n;i++)
    {
        cin>>arr[i];
    }
    ll flag=0;
    if(x%2==0)
        flag=1;
    init(1,1,n,flag);
//    cout<<tree[1]<<endl;
    while(m--)
    {

    ll p,b;
    cin>>p>>b;
    update(1,1,n,p,b,flag);
    cout<<tree[1]<<endl;

    }
    return 0;
}