Language: C++

//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; ++i)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using namespace std;
using ll = int64_t;
using ld = long double;
using P = pair<int, int>;
using vs = vector<string>;
using vi = vector<int>;
using vvi = vector<vi>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQG = priority_queue<T, vector<T>, greater<T> >;
const int INF = 100010001;
const ll LINF = (ll)INF*INF*10;
template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {return a < b && (a = b, true);}
template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {return a > b && (a = b, true);}
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second;}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << ' ' << p.second;}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, k;
    cin >> n >> k;
    vector<ll> a(n), sum(n+1), ss(n+1);
    rep(i, n) {
        cin >> a[i];
        ss[i+1] = ss[i] + a[i];
        sum[i+1] = max(sum[i], sum[i] + a[i]);
    }

    ll ans = 0;
    rep(i, n-k+1) {
        ll l = sum[i], r = sum[n] - sum[i+k], mid = max(0LL, ll(ss[i+k]-ss[i]));
        chmax(ans, l+r+mid);
    }
    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:40:56: error: no matching function for call to 'max(long long int, ll)'
   40 |         ll l = sum[i], r = sum[n] - sum[i+k], mid = max(0LL, ll(ss[i+k]-ss[i]));
      |                                                     ~~~^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:40:56: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'll' {aka 'long int'})
   40 |         ll l = sum[i], r = sum[n] - sum[i+k], mid = max(0LL, ll(ss[i+k]-ss[i]));
      |                                                     ~~~^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:40:56: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   40 |         ll l = sum[i], r = sum[n] - sum[i+k], mid = max(0LL, ll(ss[i+k]-ss[i]));
      |                                                     ~~~^~~~~~~~~~~~~~~~~~~~~~~~