CodeForces 339D Xenia and Bit Operations （线段树水题）

题意：

         给出一棵完全二叉树，从叶子到根，每层做 OR 和 XOR 的交替运算。

         问每次修改叶子后根的值。

思路：

         再简单不过的线段树。

代码：

#include <bits/stdc++.h>using namespace std;#define ls l,mid,rt*2#define rs mid+1,r,rt*2+1#define mi (l+r)/2;#define sf l,r,rtconst int MAXN=(1<<17)+100;int tree[MAXN*4],dep[MAXN*4],n,m,st,v;bool d;void push_up(int l,int r,int rt){    if(d==1)        tree[rt]=tree[rt*2]|tree[rt*2+1];    else        tree[rt]=tree[rt*2]^tree[rt*2+1];    d=!d;    return ;}void build(int l,int r,int rt){    if(l==r){        scanf("%d",&tree[rt]);        d=1;        return ;    }    int mid=mi;    build(ls);    build(rs);    push_up(sf);    return ;}void update(int l,int r,int rt){    if(l>st||r<st) return ;    if(l==r){        tree[rt]=v;        d=1;        return ;    }    int mid=mi;    update(ls);    update(rs);    push_up(sf);    return ;}int main(){    while(scanf("%d%d",&n,&m)!=-1){        n=pow(2,n);        build(1,n,1);        for(int i=0;i<m;i++){            scanf("%d%d",&st,&v);            update(1,n,1);            printf("%d\n",tree[1]);        }    }}

Xenia the beginner programmer has a sequence a, consisting of 2ⁿ non-negative integers: a₁, a₂, ..., a_2ⁿ. Xenia is currently studying bit operations. To better understand how they work, Xenia decided to calculate some value v for a.

Namely, it takes several iterations to calculate value v. At the first iteration, Xenia writes a new sequence a₁ or a₂, a₃ or a₄, ..., a_2ⁿ - 1 or a_2ⁿ, consisting of2^n - 1 elements. In other words, she writes down the bit-wise OR of adjacent elements of sequence a. At the second iteration, Xenia writes the bitwise exclusive OR of adjacent elements of the sequence obtained after the first iteration. At the third iteration Xenia writes the bitwise OR of the adjacent elements of the sequence obtained after the second iteration. And so on; the operations of bitwise exclusive OR and bitwise OR alternate. In the end, she obtains a sequence consisting of one element, and that element is v.

Let's consider an example. Suppose that sequence a = (1, 2, 3, 4). Then let's write down all the transformations (1, 2, 3, 4)  →  (1 or 2 = 3, 3 or 4 = 7)  →  (3 xor 7 = 4). The result is v = 4.

You are given Xenia's initial sequence. But to calculate value v for a given sequence would be too easy, so you are given additional m queries. Each query is a pair of integers p, b. Query p, b means that you need to perform the assignment a_p = b. After each query, you need to print the new value v for the new sequence a.

Input

The first line contains two integers n and m (1 ≤ n ≤ 17, 1 ≤ m ≤ 10⁵). The next line contains 2ⁿ integers a₁, a₂, ..., a_2ⁿ (0 ≤ a_i < 2³⁰). Each of the next m lines contains queries. The i-th line contains integers p_i, b_i (1 ≤ p_i ≤ 2ⁿ, 0 ≤ b_i < 2³⁰) — the i-th query.

Output

Print m integers — the i-th integer denotes value v for sequence a after the i-th query.

Example

Input

2 41 6 3 51 43 41 21 2

Output

1333

Note

For more information on the bit operations, you can follow this link:http://en.wikipedia.org/wiki/Bitwise_operation