#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vl  = vector<ll>;

#define REP(i,n) for(ll i=0; i<(n); ++i)

int main() {
	ll n; cin >> n;
	vl v(n); REP(i, n) cin >> v[i];
	pair<ll, ll> sum = {0,0};
	REP(i,n) {
		sum.first = max(sum.first, sum.second);
		sum.second += v[i];
		swap(sum.first, sum.second);
	}
	cout << max(sum.first, sum.second) << endl;

	return 0;
}