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#include <bits/stdc++.h>
#include <ext/numeric>
#include <unistd.h>
using namespace std;
using namespace rel_ops;
using namespace __gnu_cxx;

typedef long long ll;
typedef unsigned long long ull;
typedef unsigned uint;

#define ALL(c)          (c).begin(), (c).end()
#define REP(i, n)       for (int i = 0, $##i = (n); i < $##i; ++i)
#define FOR(i, b, e)    for (int i = (b), $##i = (e); i <= $##i; ++i)
#define FORD(i, b, e)   for (int i = (b), $##i = (e); i >= $##i; --i)
#define EACH(it, cont)  for (auto &it : cont)
#define ever ( ; ; )
#define skip continue
const int inf = 1000000001;

struct GetSizeHelper {
	int s;
	operator int () const { return s; }
	template<class T> GetSizeHelper(const T &t) : s((int) t.size()) {}
};
#define SIZE (GetSizeHelper)

template<class T> int unique(T &t, bool sorted = false) {
	if (!sorted) { sort(ALL(t)); }
	t.resize(unique(ALL(t)) - t.begin()); 
	return SIZE t;
}
template <class T, class U> bool remin(T &a, const U &b) { return b < a ? a = b, true : false; }
template <class T, class U> bool remax(T &a, const U &b) { return b > a ? a = b, true : false; }
template<class T> T fromString(const string &s) { T t; istringstream(s) >> t; return t; }
template<class T> string toString(const T &t) { ostringstream oss; oss << t; return oss.str(); }
struct StdinReader {
	StdinReader() { ios::sync_with_stdio(0); }
} stdinReader;
#define get stdinReader,

#ifndef KOO_AFL
template<class T> StdinReader &operator, (StdinReader &sr, T &t) { cin >> t; return sr; }
#else // BINARY_INPUT
template<class T> StdinReader &operator, (StdinReader &sr, T &t) { assert(sizeof(t) <= 8); read(0, &t, sizeof(t)) ; return sr; }
#endif

template<class T> StdinReader &operator, (StdinReader &sr, vector<T> &v) {
	for (auto &x : v) { sr, x; } return sr;
}
#define dump     fancy_dumper::DumpFirst<&std::cerr>(),
#define say      fancy_dumper::DumpFirst<&std::cout>(),
#define $dump    fancy_dumper::Dumper<&std::cerr>
#define $say     fancy_dumper::Dumper<&std::cout>
#ifndef $
#define $(x) #x, fancy_dumper::ToggleSeparator(), (x),\
                 fancy_dumper::ToggleSeparator()
#endif

namespace fancy_dumper {

struct ToggleSeparator { };

template<ostream *Out>
struct DumpFirst { };

template<ostream *Out>
struct Dumper {
	static void *&last() {
		static void *p;
		return p;
	}
	static const char *&separator() {
		static const char *s = " ";
		return s;
	}
	static const char *&separatorNewLine() {
		static const char *s = "\n";
		return s;
	}
	static const char *&unseparator() {
		static const char *s = "=";
		return s;
	}
	Dumper() {
		last() = this;
	}
	~Dumper() {
		if (this == last()) {
			*Out << separatorNewLine();
			last() = 0;
		}
	}
	Dumper operator, (ToggleSeparator) {
		std::swap(separator(), unseparator());
		return Dumper();
	}
};

template<ostream *Out, class T>
Dumper<Out> operator,(Dumper<Out>, const T &e) {
	*Out << Dumper<Out>::separator() << e;
	return Dumper<Out>();
}

template<ostream *Out, class T>
Dumper<Out> operator, (DumpFirst<Out>, const T &e) {
	*Out << e;
	return Dumper<Out>();
}

}

template<class T, class Y>
ostream &operator<< (ostream &o, const pair<T, Y> &p) {
	return o << p.first << ' ' << p.second;
}

template<class T>
ostream &operator<< (ostream &o, const vector<T> &v) {
	bool isBegin = true;
	EACH (e, v) {
		if (!isBegin) { o << ' '; }
		isBegin = false;
		o << e;
	}
	return o;
}

template<class T>
ostream &operator<< (ostream &o, const set<T> &v) {
	bool isBegin = true;
	EACH (e, v) {
		if (!isBegin) { o << ' '; }
		isBegin = false;
		o << e;
	}
	return o;
}

template<class T>
ostream &operator,(ostream &o, const T &t) {
	return o << t;
}
// code starts here


#include "kanapka.h"
#include "message.h"

int N = GetN();

struct Solution {
	ll sum, pref, suff, alone;
	Solution() { memset(this, 0, sizeof(Solution)); }
	void solve(int beg, int end);
	void merge(const Solution &right);
};

void send(int to, const Solution &sol) {
	PutLL(to, sol.sum);
	PutLL(to, sol.pref);
	PutLL(to, sol.suff);
	PutLL(to, sol.alone);
	Send(to);
}

void recv(int ot, Solution &my) {
	static Solution right;
	Receive(ot);
	right.sum = GetLL(ot);
	right.pref = GetLL(ot);
	right.suff = GetLL(ot);
	right.alone = GetLL(ot);
	my.merge(right);
}

int main() {
	int workers = NumberOfNodes();
	int me = MyNodeId();
	
	int m = N / workers + 1;
	Solution my;
	my.solve(me*m, (me+1)*m);
	
	for (int mask = 1; ; mask <<= 1) {
		int a = me | mask;
		int b = me & ~mask;
		if (a == me) {
			send(b, my);
			break;
		} else {
			if (a < workers) {
				recv(a, my);
			} else if (!me) {
				break;
			}
		}
	}
	
	if (!me) {
		say my.sum + my.alone;
	}
}

void Solution::merge(const Solution &right) {
	remax(alone, max(suff+right.pref, right.alone));
	remax(pref, right.pref-sum);
	suff = max(right.suff, suff-right.sum);
	sum += right.sum;
}

void Solution::solve(int beg, int end) {
	remin(end, N);
	if (beg >= end) {
		return;
	}
	
	ll curr = 0;
	FOR (i, beg, end-1) {
		ll tmp = GetTaste(ll(i));
		sum += tmp;
		curr -= tmp;
		remax(alone, curr);
		remax(pref, -sum);
		remax(curr, 0);
	}
	curr = 0;
	FORD (i, end-1, beg) {
		curr -= GetTaste(ll(i));
		remax(suff, curr);
	}
}