#include"bits/stdc++.h"
using namespace std;
using ll = long long;
using ld = long double;
#define rep(i,m,n) for(ll i=(ll)m;i<(ll)n;i++)
#define Endl endl
#define pr(i,j) make_pair(i,j) 
const ll mod = 998244353;
const ll inf = 5e18;
const ld pi = 3.14159265358979;
int main() {
	ll n;
	cin >> n;
	vector<vector<ll>>dp(n, vector<ll>(2,inf));
	vector<ll>v(n);
	rep(i, 0, n)cin >> v[i];
	dp[0][0] = 0;
	dp[0][1] = v[0];
	rep(i, 1, n) {
		dp[i][0] = max(dp[i - 1][0], dp[i - 1][1]);
		dp[i][1] = dp[i - 1][0] + v[i];
	}
	cout << max(dp[n - 1][0], dp[n - 1][1]) << endl;
}