Language: C++

#include<iostream>
#include<string>
#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<deque>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
typedef vector<int> vec;
typedef vector<vector<int>> mat;
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define pb push_back
#define debug(x)  cout << #x << " = " << (x) << endl;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
#define int long long

//pair<値,位置のインデックス>でソートしておけば、位置がわかる！！
//大きい順、小さい順にみて、データ構造をうまく使い計算量を減らす
//XについてYを数えたものの合計を、YについてXを数えたものの合計と言い換える

void solve() {
	int n; cin >> n;
    vector<P> p(n);
    rep(i, n) {
        int x; cin >> x;
		p[i] = P(x, i);
    }
	sort(all(p));
	reverse(all(p));
	//自分より大きいもの位置さえわかれば良さそう
	//大きい順に考えればok
	int ans = 0;
	set<int> se;
	se.insert(-1);
	se.insert(n);
    rep(i, n) {
		int y = p[i].fr, k = p[i].sc;
		se.insert(k);
		auto ite = se.lower_bound(k);
		auto mi = ite - 2, ma = ite + 2;
		ans += y * (*ma - *mi - 1);
	}
	cout << ans << endl;
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//init();
	solve();
	//cout << "finish" << endl;
    return 0;
}

Compiler output:
a.cc: In function 'void solve()':
a.cc:77:31: error: no match for 'operator-' (operand types are 'std::_Rb_tree_const_iterator<long long int>' and 'int')
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                           ~~~ ^ ~
      |                           |     |
      |                           |     int
      |                           std::_Rb_tree_const_iterator<long long int>
In file included from /usr/include/c++/14/string:48,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:77:33: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::reverse_iterator<_Iterator>'
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                                 ^
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:77:33: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::move_iterator<_IteratorL>'
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                                 ^
In file included from a.cc:16:
/usr/include/c++/14/complex:370:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&, const complex<_Tp>&)'
  370 |     operator-(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:370:5: note:   template argument deduction/substitution failed:
a.cc:77:33: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::complex<_Tp>'
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                                 ^
/usr/include/c++/14/complex:379:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&, const _Tp&)'
  379 |     operator-(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:379:5: note:   template argument deduction/substitution failed:
a.cc:77:33: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::complex<_Tp>'
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                                 ^
/usr/include/c++/14/complex:388:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const _Tp&, const complex<_Tp>&)'
  388 |     operator-(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:388:5: note:   template argument deduction/substitution failed:
a.cc:77:33: note:   mismatched types 'const std::complex<_Tp>' and 'int'
   77 |                 auto mi = ite - 2, ma = ite + 2;
      |                                 ^
/usr/include/c++/14/complex:465:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&)'
  465 |     operator-(const complex<_Tp>& __x)
      |     ^~~~~~~~
/usr/include/c++/14/complex:465:5: note:   candidate expects 1 argument, 2 provided
a.cc:78:30: error: 'ma' was not declared in this scope; did you mean 'mat'?
   78 |                 ans += y * (*ma - *mi - 1);
      |                              ^~
      |                              mat