#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int n;
int dp[1123][2];
int v[1123];

int main() {
	cin >> n;
	REP(i, n) scanf("%d", v + i);
	
	memset(dp, -1, sizeof(dp));
	dp[0][0] = dp[0][1] = 0;
	
	REP(i, n) {
		chmax(dp[i + 1][0], dp[i][1]);
		
		chmax(dp[i + 1][1], dp[i][0] + v[i]);
		chmax(dp[i + 1][0], dp[i][0]);
	}
	
	cout << max(dp[n][0], dp[n][1]) << endl;
	
	return 0;
}