本题是线段树板子题，简单维护一下即可

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

const int N = 100010;

struct Node{
    LL sum;
    LL tag;
}seg[N * 4];

int n, m;
LL a[N];

void pushup(int u){
    seg[u].sum = seg[u << 1].sum + seg[u << 1 | 1].sum;
}
void pushdown(int u, int l, int r){
    LL &x = seg[u].tag;
    seg[u << 1].tag += x;
    seg[u << 1 | 1].tag += x;
    int mid = l + r >> 1;
    seg[u << 1].sum += 1ll *(mid - l + 1) * x;
    seg[u << 1 | 1].sum += 1ll * (r - (mid + 1) + 1) * x;
    seg[u].tag = 0;//x = 0;
}
void build(int u, int l, int r){
    if(l == r){
        seg[u].sum = a[l];
        seg[u].tag = 0;
        return;
    }
    int mid = l + r >> 1;
    build(u << 1, l, mid);build(u << 1 | 1, mid + 1, r);
    pushup(u);
}
void modify(int u, int l, int r, int ql, int qr, int x){
    if(l == ql && r == qr){
        seg[u].tag += x;
        seg[u].sum += 1ll * (r - l + 1) * x;
        return;
    }
    pushdown(u, l, r);
    int mid = l + r >> 1;
    if(qr <= mid) modify(u << 1, l, mid, ql, qr, x);
    else if(ql > mid) modify(u << 1 | 1, mid + 1, r, ql, qr, x);
    else{
        modify(u << 1, l, mid, ql, mid, x);
        modify(u << 1 | 1, mid + 1, r, mid + 1, qr, x);
    } 
    pushup(u);
}
LL query(int u, int l, int r, int ql, int qr){
    if(l == ql  && r == qr){
        return seg[u].sum;
    }   
    pushdown(u, l, r);
    int mid = l + r >> 1;
    if(qr <= mid) return query(u << 1, l, mid, ql, qr);
    else if(ql > mid) return query(u << 1 | 1, mid + 1, r, ql, qr);
    else{
        return query(u << 1, l, mid, ql, mid) + query(u << 1 | 1, mid + 1, r, mid + 1, qr);
    }
    // pushup(u);
}

int main(){
    int a, b; cin >> a >> b;
    build(1, 1, 1000);
    modify(1, 1, 1000, 1, 1, a);
    modify(1, 1, 1000, 2, 2, b);
    cout << query(1, 1, 1000, 1, 2) << endl;

}