Shared code

#include <bits/stdc++.h>

#define range(it, a, b) for (ll it = a; it < b; it++)
#define all(x) begin(x), end(x)
#define ll long long
#define ull unsigned long long
#define INF64 ((ll) 1 << 60)
#define INF32 (1 << 30)
#define mset multiset
#define uset unordered_set
#define umap unordered_map 
#define pqueue priority_queue 
#define ptr(A) shared_ptr<A>

using namespace std;

void setio (string name) {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    if (name.size()) {
        freopen((name + ".in").c_str(), "r", stdin);
        freopen((name + ".out").c_str(), "w", stdout);
    }
}

struct SegTree {
    struct Node {
        ptr(Node) left, right;
        ll l, r, max, pre, suf, sum;

        ll get_l () { return (l + r) / 2; }
        ll get_r () { return get_l() + 1; }
    };

    vector<ll>& arr;
    ptr(Node) root;

    SegTree(vector<ll>& a) : arr(a) {
        root = ptr(Node) (new Node);
        root->l = 0;
        root->r = a.size() - 1;
        build(root);
    }

    void build (ptr(Node) node) {
        if (node->l == node->r) {
            node->max = arr[node->l];
            node->pre = node->max;
            node->suf = node->max;
            node->sum = node->max;
            return;
        }

        node->left = ptr(Node) (new Node);
        node->left->l = node->l;
        node->left->r = node->get_l();
        build(node->left);

        node->right = ptr(Node) (new Node);
        node->right->l = node->get_r();
        node->right->r = node->r;
        build(node->right);

        node->max = max({node->left->max, node->right->max, node->left->suf + node->right->pre});
        node->sum = node->left->sum + node->right->sum;
        node->pre = max(node->left->pre, node->left->sum + node->right->pre);
        node->suf = max(node->right->suf, node->right->sum + node->left->suf);
    }

    void update(ll i, ll d, ptr(Node) node) {
        if (node->l == node->r) {
            node->max = d;
            node->pre = node->max;
            node->suf = node->max;
            node->sum = node->max;
            return;
        }

        if (i <= node->get_l())
            update(i, d, node->left);
        if (node->get_r() <= i) 
            update(i, d, node->right);
        
        node->max = max({node->left->max, node->right->max, node->left->suf + node->right->pre});
        node->sum = node->left->sum + node->right->sum;
        node->pre = max(node->left->pre, node->left->sum + node->right->pre);
        node->suf = max(node->right->suf, node->right->sum + node->left->suf);
    }

    ll update(ll i, ll d) {
        update(i, d, root);
        return root->max;
    }
};

ll n, q;

void solve() {
    cin >> n >> q;

    vector<ll> arr(n);
    range(i, 0, n) 
        cin >> arr[i];
    
    SegTree st (arr);
    while (q--) {
        ll k, x;
        cin >> k >> x;
        k--;
        cout << max(0ll, st.update(k, x)) << '\n';
    }
}

int main () {
    setio("");
    ll t = 1; 
    // cin >> t;
    while (t--) solve();
}

// IT'S TOUGH, I KNOW
// BUT YOU'D RATHER DIE FIGHTING THAN LIVE ON YOUR KNEES
// THOUGH YOU WON'T DO NEITHER OF THOSE
// IMPOSSIBLE, AS IT'S AGAINST YOUR NATURE
// AS YOU ALREADY WON
// I SEE YOUR MEDAL HANGING FROM YOUR NECK
// SHINING AS NOTHING YOU'VE EVER HAD

// THOUSANDS AND THOUSANDS OF LINES
// YOU AREADY MADE IT THIS FAR
// WHO COULD TELL HOW FAR YOU WILL GET
// BUT YOU... ?

// THEN COME ON, YOU BASTARD!
// GO CLEAR YOUR MIND AND STAND
// AS EACH OF THOSE LINES IS A STEP CLOSER
// CLOSER TO THE GREATNESS YOU PURSUE