#include <cassert>
#include <functional>
#include <set>
#include <ctime>
#include <cmath>
#include <climits>
#include <cstring>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <algorithm>
#include <iostream>
#include <cstdio>
#ifndef ONLINE_JUDGE
# include <complex>
# include <random>
# include <array>
# define mkt make_tuple
#endif
#ifdef _LOCAL
# include "for_local.h"
#else
# define ifdebug if (false)
# define echo ((void)0)
#endif
using namespace std;
typedef unsigned int uint; typedef long long ll; typedef unsigned long long ull;
#define repi(_I, _B, _E) for(int _I = (_B); (_I) < (_E); ++ (_I))
#define rep(_I, _N) for(int _I = 0; (_I) < (_N); ++ (_I))
#define all(_X) (_X).begin(), (_X).end()
#define mkp make_pair
inline int scani() { int n; scanf(" %d", &n); return n; }

#define MEMOIZE(_Args, _Expr) do { auto&& _args = (std::make_tuple _Args); static std::map<typename std::remove_reference<decltype(_args)>::type, typename std::remove_reference<decltype(_Expr)>::type> _memo; auto&& _it = _memo.lower_bound(_args); if ( _it == _memo.end() || _it->first != _args ) { return _memo.emplace_hint(_it, std::move(_args), (_Expr))->second; } else { return _it->second; } } while(false)

int n;
vector<int> vs;

int solve(int i)
{
	if ( i >= n ) return 0;
	MEMOIZE((i),
		max(vs[i] + solve(i + 2), solve(i + 1))
		);
}

signed main()
{
	cin >> n;
	vs.resize(n);
	rep(i, n) cin >> vs[i];
	cout << solve(0) << endl;

	return 0;
}