显而易见的，这是一道线段树模板题

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

struct node
{
    int l, r;
    int v;
}tr[4 * 500005];
int w[500005];
void pushup(node& curr, node& left, node& right)
{
    curr.v = left.v + right.v;
}

void pushup(int u)
{
    node left = tr[u << 1];
    node right = tr[u << 1 | 1];
    pushup(tr[u], left, right);
}

void build(int u, int l, int r)
{
    tr[u] = { l,r };
    if (l == r)
    {
        tr[u] = { l, r, w[r] };
        return;
    }
    int mid = l + r >> 1;
    build(u << 1, l, mid), build(u << 1 | 1, mid + 1, r);
    pushup(u);
}

node query(int u, int l, int r)
{
    if (l <= tr[u].l && r >= tr[u].r)return tr[u];
    int mid = tr[u].l + tr[u].r >> 1;
    if (r <= mid)return query(u << 1, l, r);
    else if (l > mid)return query(u << 1 | 1, l, r);
    else
    {
        node left = query(u << 1, l, r);
        node right = query(u << 1 | 1, l, r);
        node res;
        pushup(res, left, right);
        return res;
    }
}

void solve()
{
    for (int i = 1; i <= 2; i++)cin >> w[i];
    build(1, 1, 2);
    cout << query(1, 1, 2).v << "\n";
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int tt = 1;
    //cin >> tt;
    while (tt--)solve();
    return 0;
}

用主席树感觉更优雅(bushi

还没学（

主要是发现大家竟然都不用线段树做，线段树会难过的（bushi

好活hhhh

A+B,最好的解法是splay吧

不会splayQ^Q

不会splay ｡ﾟ･ (⁄ ⁄>⁄ ︿ ⁄<⁄ ⁄) ･ﾟ｡