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#include <algorithm>
#include <iostream>
#include <vector>
#include "kanapka.h"
#include "message.h"

using namespace std;


#define log if (false) cerr
typedef long long ll;
typedef unsigned long long ull;

const ll PARALLEL_TRIGGER = 10000000;


struct Tastes
{
    ll maxLeft;
    ll maxRight;
    ll maxBoth;
    ll total;

    Tastes() : maxLeft(0), maxRight(0), maxBoth(0), total(0)
    {}
};

struct LocalMax
{
    int index;
    ll taste;
};


Tastes computeTastes(int fromN, int toN)
{
    Tastes tastes;
    ll total = 0;

    for (int i = fromN; i < toN; i++)
    {
        total += GetTaste(i);
    }

    ll maxLeft = 0;
    ll maxRight = max(0LL, total);
    ll maxBoth = maxRight;
    ll sumLeft = 0;
    ll sumRight = total;

    for (int i = fromN; i < toN; i++)
    {
        ll taste = GetTaste(i);
        sumLeft += taste;
        sumRight -= taste;
        maxLeft = max(maxLeft, sumLeft);
        maxRight = max(maxRight, sumRight);
        maxBoth = max(maxBoth, maxLeft + sumRight);

        log << sumLeft << ", " << sumRight << " - " << maxLeft << ", " << maxRight;
        log << ", " << maxBoth << endl;
    }

    tastes.maxLeft = maxLeft;
    tastes.maxRight = maxRight;
    tastes.maxBoth = maxBoth;
    tastes.total = total;

    return tastes;
}

void sendTastes(const Tastes& tastes)
{
    PutLL(0, tastes.maxLeft);
    PutLL(0, tastes.maxRight);
    PutLL(0, tastes.maxBoth);
    PutLL(0, tastes.total);
    Send(0);
}

Tastes receiveTastes(ll nodeId)
{
    Tastes tastes;
    Receive(nodeId);
    tastes.maxLeft = GetLL(nodeId);
    tastes.maxRight = GetLL(nodeId);
    tastes.maxBoth = GetLL(nodeId);
    tastes.total = GetLL(nodeId);
    return tastes;
}

ll mergeTastes(ll numberOfNodes)
{
    Tastes result;
    vector<Tastes> allTastes;

    for (ll i = 0; i < numberOfNodes; i++)
    {
        allTastes.push_back(receiveTastes(i));
    }

    ll total = 0;
    for (unsigned i = 0; i < allTastes.size(); i++)
    {
        total += allTastes[i].total;
    }

    ll maxLeft = 0;
    ll maxRight = max(0LL, total);
    ll maxBoth = maxRight;
    ll sumLeft = 0;
    ll sumRight = total;

    for (unsigned i = 0; i < allTastes.size(); i++)
    {
        Tastes tastes = allTastes[i];

        maxBoth = max(maxBoth, maxLeft + sumRight-tastes.total + tastes.maxRight);

        maxLeft = max(maxLeft, sumLeft + tastes.maxLeft);

        sumLeft += tastes.total;
        sumRight -= tastes.total;

        maxRight = max(maxRight, sumRight + tastes.maxRight);

        maxBoth = max(maxBoth, sumLeft-tastes.total + sumRight + tastes.maxBoth);

        log << sumLeft << ", " << sumRight << " - " << maxLeft << ", " << maxRight;
        log << ", " << maxBoth << endl;
    }


    return maxBoth;
}


int _main()
{
    if (MyNodeId() == 0)
    {
        ll n = GetN();
        Tastes tastes = computeTastes(0, n);
        cout << tastes.maxBoth;
    }
    return 0;
}

int main()
{
    ll n = GetN();
    if (n < PARALLEL_TRIGGER)
    {
        _main();
        return 0;
    }
    ll myNodeId = MyNodeId();
    ll numberOfNodes = NumberOfNodes();

    ll from = myNodeId * n / numberOfNodes;
    ll to = (myNodeId + 1) * n / numberOfNodes;

    Tastes tastes = computeTastes(from, to);
    sendTastes(tastes);

    if (myNodeId == 0)
    {
        ll result = mergeTastes(numberOfNodes);
        cout << result;
    }

    return 0;
}