Goldilocks (coordinate compression)

#include <iostream>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <regex>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <unordered_map>
#include <numeric>
#include <iomanip>
using namespace std;
#define pii pair<int, int>
#define ll long long
#define FAST ios_base::sync_with_stdio(false); cin.tie(NULL)
#define mp(x1, x2) ( make_pair(x1, x2) )
const int dx[4] = {1, 0, 0, -1}, dy[4] = {0, 1, -1, 0};
const int dl[2] = {1, -1};
const int MOD = 100000007;
const int MAXN = 202020;

int n, x, y, z;
pii arr[MAXN];
vector<int> v;
int changes[MAXN * 3];
int milk[MAXN * 3];

int main(){
    FAST;
    //freopen("milktemp.in", "r", stdin);
    //freopen("milktemp.out", "w", stdout);
    cin >> n >> x >> y >> z;
    for (int i = 0; i < n; i++) {
        cin >> arr[i].first >> arr[i].second;
        arr[i].second++;
        v.push_back(arr[i].first);
        v.push_back(arr[i].second);
    }
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    for (int i = 0; i < n; i++) {
        arr[i].first = lower_bound(v.begin(), v.end(), arr[i].first) - v.begin();
        arr[i].second = lower_bound(v.begin(), v.end(), arr[i].second) - v.begin();
        changes[arr[i].first] += y - x;
        changes[arr[i].second] += z - y;
    }
    milk[0] = x * n + changes[0];
    //cout << milk[0] << endl;
    int ans = milk[0];
    for (int i = 1; i < 3 * n; i++) {
        milk[i] = milk[i - 1] + changes[i];
        ans = max(ans, milk[i]);
        //cout << i << " " << milk[i] << endl;
    }
    cout << ans << endl;
}