#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n;
	cin >> n;

	vector<int> v(n);
	rep(i, n) cin >> v[i];

	int INF = 1e9;
	int dp[n+1][2];
	rep(i, n+1) rep(j, 2) dp[i][j] = -INF;
	dp[0][0] = 0;

	rep(i, n){
		if(dp[i][0] != -INF) chmax(dp[i+1][0], dp[i][0]);
		if(dp[i][1] != -INF) chmax(dp[i+1][0], dp[i][1]);
		if(dp[i][0] != -INF) chmax(dp[i+1][1], dp[i][0] + v[i]);
	}

	cout << max(dp[n][0], dp[n][1]) << endl;
}