MLE了，求卡常。

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cassert>
#include <iostream>
using namespace std;
#define lcc t[k].lc
#define rcc t[k].rc
typedef long long ll;
struct node{
    ll sum, ls;
    int val, lc, rc;
    bool tag;
}t[4500005];
int cnt = 1, n;
void push_up(int k){
    t[k].val = -1;
    t[k].sum = t[t[k].lc].sum + t[t[k].rc].sum;
    t[k].ls = max(t[t[k].lc].ls, t[t[k].rc].ls + t[t[k].lc].sum);
    return;
}
void push_down(int k, int l, int r){
    int mid = l + r >> 1;
    if(t[k].lc == 0) t[k].lc = ++cnt;
    if(t[k].rc == 0) t[k].rc = ++cnt;


    if(!t[k].tag)return;
    t[k].tag = 0; t[lcc].tag = t[rcc].tag = 1;
    t[lcc].sum = (t[lcc].val = t[k].val) * (mid - l + 1);
    t[rcc].sum = (t[rcc].val = t[k].val) * (r - mid);
    if(t[lcc].sum > 0) t[lcc].ls = t[lcc].sum;
    else t[lcc].ls = t[k].val;
    if(t[rcc].sum > 0) t[rcc].ls = t[rcc].sum;
    else t[rcc].ls = t[k].val;
    return;
}
void add(int k, int l, int r, int x, int y, ll z){
    if(l > y or r < x) return;
    if(l >= x and r <= y){
        t[k].tag = 1;
        t[k].sum = (r - l + 1) * (t[k].val = z);
        t[k].ls = t[k].sum > 0 ? t[k].sum : t[k].val;
        return;
    }
    int mid = l + r >> 1;
    push_down(k, l, r);
    if(x <= mid) add(t[k].lc, l, mid, x, y, z);
    if(y > mid) add(t[k].rc, mid+1, r, x, y, z);
    push_up(k);
}
int ask(int k, int l, int r, ll high){
    if(high >= t[k].ls) return r;
    if(t[k].val != -1) return l + (high / t[k].val) - 1;
    int mid = l + r >> 1;
    return high >= t[t[k].lc].ls ? ask(t[k].rc, mid + 1, r, high - t[t[k].lc].sum) : ask(t[k].lc, l, mid, high);
}
int main(){
    cin >> n; char s;
    for(int x, y, z; cin >> s and s != 'E';){
        if(s == 'I'){cin >> x >> y >> z; add(1, 1, n, x, y, z);}
        else {cin >> x;cout << ask(1, 1, n, x) << '\n';}
    }
    return 0;
}