Sement tree GCD from L to R

#include "bits/stdc++.h"
using namespace std;
typedef long long int ll;
const int N = 2e6;
ll arr[N], tree[N], level;
#define C(x) cout << x << ' '
#define L '\n'
void build(ll start, ll endd, ll seg_tree_index){

    if(start == endd){
        tree[seg_tree_index] = arr[start];
        return ;
    }
    ll mid = (start + endd) >> 1;
    build(start, mid, 2 * seg_tree_index);
    build(mid + 1, endd, 2 * seg_tree_index + 1);

    tree[seg_tree_index] = __gcd(tree[2 * seg_tree_index], tree[2 * seg_tree_index + 1]);
}

int query(int l, int r, int ql, int qr, int seg_tree_index){
    // C(l);C(r);C(ql);C(qr);C(L);
    if(r < ql || l > qr)return 0;
    if(ql <= l && qr >= r)return tree[seg_tree_index];
    int mid = (l+r) >> 1;
    return __gcd(query(l, mid, ql, qr, 2 * seg_tree_index), query(mid + 1, r, ql, qr, 2 *                   seg_tree_index + 1));
}

/*
void update(ll l, ll r,ll pos, ll val, ll seg_tree_index, ll fl){
    if(l <= pos && r >= pos){ // Think some other way after AC bout this condition
    if(l == r && l == pos){
        tree[seg_tree_index] = val;
        return;
    }
    ll mid = (l + r) >> 1;
    update(l, mid, pos, val, 2 * seg_tree_index, fl );
    update(mid + 1, r, pos, val, 2 * seg_tree_index + 1, fl );
    }
    else
    return;
}*/
int main(){
ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
    ll n, i, q, ql, qr;
    cin >> n;// >> q;
        for(i = 1; i <= n; i++)
    cin >> arr[i];

    build(1, n, 1);

    //for(i = 1; tree[i]; i++)
   // cout << tree[i] << ' ';
    cout << endl;
   cout << query(1, n, 1, 2, 1);


    return 0;
}