Language: C++

//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;
typedef long double lb;
#define int long long
#define double long double
#define endn "\n"
typedef pair<int,int> P;
template<class T> inline bool chmin(T& a, T b){if(a>b){a = b;return 1;}return 0;}
template<class T> inline bool chmax(T& a, T b){if(a<b){a = b;return 1;}return 0;}
const int MOD = 1000000007;
//const int MOD = 998244353;
template<class T> inline int add(T& a, T b, T M = MOD){a=(a+M)%M;b=(b+M)%M;a=(a+b)%M;return a;};
template<class T> inline int mul(T& a, T b, T M = MOD){if(a>=M)a%=M;if(b>=M)b%=M;a*=b;if(a>=M)a%=M;return a;};
const ll INF = 1e16;
const double EPS = 1e-10;
const double PI = 3.141592653589793;
const string abc="abcdefghijklmnopqrstuvwxyz";
const string ABC="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const pair<int,int> fd[] = {make_pair(1,0),make_pair(-1,0),make_pair(0,1),make_pair(0,-1)}; 

////////////////////////////////////////////////////////////////////
///////////////////////___modpow___////////////////////
ll modpow(ll a,  ll n, const ll &MOD = MOD){
  ll ret = n == 0 ? 1 : modpow(a, n/2, MOD);
  (ret *= ret) %= MOD;
  if(n%2)((ret *= a) %= MOD);
  return ret;
}
///////////////////////___modinv___////////////////////
ll modinv(ll d, const ll &MOD = MOD){
  return modpow(d, MOD-2, MOD);
}
////////////////////////////////////////////////////////////////////

int n, dp[2100][2100];P a[2100];
signed main() {
  cin>>n;rep(i,n)cin>>a[i].first, a[i].second = i;
  sort(a,a+n,greater<int>());
  dp[0][1] = a[0].first*a[0].second;
  dp[0][0] = a[0]*(n-a[0].second-1);
  repd(i,1,n){
    rep(j,n){
      dp[i][j] = max(dp[i-1][j]+a[i]*(n-a[i].second-1), dp[i-1][j-1]+a[i]*(a[i].second-j));
    }
  }
  int ans = 0;
  rep(i,n)chmax(ans, dp[n-1][i]);
  cout << ans << endl;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:44:18: error: no match for 'operator*' (operand types are 'P' {aka 'std::pair<long long int, long long int>'} and 'long long int')
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |              ~~~~^~~~~~~~~~~~~~~~~~
      |                 |               |
      |                 |               long long int
      |                 P {aka std::pair<long long int, long long int>}
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:2:
/usr/include/c++/14/complex:400:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const complex<_Tp>&)'
  400 |     operator*(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:400:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::complex<_Tp>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/complex:409:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const _Tp&)'
  409 |     operator*(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:409:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::complex<_Tp>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/complex:418:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const _Tp&, const complex<_Tp>&)'
  418 |     operator*(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:418:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   mismatched types 'const std::complex<_Tp>' and 'long long int'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'long long int'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'long long int'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::valarray<_Tp>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::valarray<_Tp>'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:44:35: note:   mismatched types 'const std::valarray<_Tp>' and 'long long int'
   44 |   dp[0][0] = a[0]*(n-a[0].second-1);
      |                                   ^
a.cc:47:37: error: no match for 'operator*' (operand types are 'P' {aka 'std::pair<long long int, long long int>'} and 'long long int')
   47 |       dp[i][j] = max(dp[i-1][j]+a[i]*(n-a[i].second-1), dp[i-1][j-1]+a[i]*(a[i].second-j));
      |                                 ~~~~^~~~~~~~~~~~~~~~~~
      |                                    |               |
      |                                    |               long long int
      |                                    P {aka std::pair<long long int, long long int>}
/usr/include/c++/14/complex:400:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const complex<_Tp>&)'
  400 |     operator*(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:400:5: note:   template argument deduction/substitution failed:
a.cc:47:54: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::complex<_Tp>'
   47 |       dp[i][j] = max(dp[i-1][j]+a[i]*(n-a[i].second-1), dp[i-1][j-1]+a[i]*(a[i].second-j));
      |                                                      ^
/usr/include/c++/14/complex:409:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const _Tp&)'
  409 |     operator*(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:409:5: note:   template argument deduction/substitution failed:
a.cc:47:54: note:   'P' {aka 'std::pair<long long int, long long int>'} is not derived from 'const std::complex<_Tp>'
   47 |       dp[i][j] = max(dp[i-1][j]+a[i]*(n-a[i].second-1), dp[i-1][j-1]+a[i]*(a[i].second-j));
      |                                                      ^
/usr/include/c++/14/complex:418:5: note: candidate: 'template<class _