Language: C++

#include <bits/stdc++.h>
using namespace std;
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename T> using gpp_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename L> using gpp_map = tree<T, L, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T> using gpp_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;*/
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin);i<(end);i++)
#define REP(i, n) FOR(i,0,n)
#define IFOR(i, begin, end) for(int i=(end)-1;i>=(begin);i--)
#define IREP(i, n) IFOR(i,0,n)
#define Sort(v) sort(v.begin(), v.end())
#define Reverse(v) reverse(v.begin(), v.end())
#define all(v) v.begin(),v.end()
#define SZ(v) ((int)v.size())
#define Lower_bound(v, x) distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) distance(v.begin(), upper_bound(v.begin(), v.end(), x))
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
#define bit(n) (1LL<<(n))
#define bit_exist(x, n) ((x >> n) & 1)
#define debug(x) cout << #x << "=" << x << endl;
#define vdebug(v) cout << #v << "=" << endl; REP(i_debug, v.size()){ cout << v[i_debug] << ","; } cout << endl;
#define mdebug(m) cout << #m << "=" << endl; REP(i_debug, m.size()){ REP(j_debug, m[i_debug].size()){ cout << m[i_debug][j_debug] << ","; } cout << endl;}
#define pb push_back
#define f first
#define s second
#define int long long
#define INF 1000000000000000000
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < v.size(); i++) { cout << v[i]; if(i != v.size() - 1) cout << endl; }; return os; }
template<typename T> void Out(T x) { cout << x << endl; }
template<typename T1, typename T2> void Ans(bool f, T1 y, T2 n) { if(f) Out(y); else Out(n); }

using vec = vector<int>;
using mat = vector<vec>;
using Pii = pair<int, int>;
using PiP = pair<int, Pii>;
using PPi = pair<Pii, int>;
using bools = vector<bool>;
using pairs = vector<Pii>;

//int dx[4] = {1,0,-1,0};
//int dy[4] = {0,1,0,-1};
//char d[4] = {'D','R','U','L'};

const int mod = 1000000007;
//const int mod = 998244353;
//#define Add(x, y) x = (x + (y)) % mod
//#define Mult(x, y) x = (x * (y)) % mod



signed main(){

    int N; cin >> N;
    vec L(N), R(N);
    pairs p(N);
    REP(i, N){
        cin >> L[i] >> R[i];
        p[i] = Pii(L[i], i);
    }
    Sort(p);

    vec maxL1(N), maxL2(N), minR1(N), minR2(N);
    maxL1[0] = L[p[0].s], minR1[0] = R[p[0].s];
    FOR(i, 1, N){
        int i0 = p[i].s;
        maxL1[i] = max(maxL1[i - 1], L[i0]);
        minR1[i] = min(minR1[i - 1], R[i0]);
    }

    maxL2[N - 1] = L[p[N - 1].s], minR2[N - 1] = R[p[N - 1].s];
    IFOR(i, 0, N - 1){
        int i0 = p[i].s;
        maxL2[i] = max(maxL2[i + 1], L[i0]);
        minR2[i] = min(minR2[i + 1], R[i0]);
    }
    int ans = 0;
    REP(i, N - 1){
        int a1 = minR1[i] - maxL1[i] + 1, a2 = minR2[i + 1] - maxL2[i + 1] + 1;
        Max(ans, max(a1, 0LL) + max(a2, 0LL));
    }

    int a = max(maxR1[N - 1] - minL1[N - 1] + 1, 0LL);
    REP(i, N) Max(ans, a + R[i] - L[i] + 1);

    Out(ans);

    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:87:17: error: 'maxR1' was not declared in this scope; did you mean 'maxL1'?
   87 |     int a = max(maxR1[N - 1] - minL1[N - 1] + 1, 0LL);
      |                 ^~~~~
      |                 maxL1
a.cc:87:32: error: 'minL1' was not declared in this scope; did you mean 'minR1'?
   87 |     int a = max(maxR1[N - 1] - minL1[N - 1] + 1, 0LL);
      |                                ^~~~~
      |                                minR1