#include"bits/stdc++.h"
//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
typedef long long ll;
//const int mod = 1e9 + 7;
int n;
int v[1002];
int dp[1002][2];

int dfs(int m, bool flag) {
	if (dp[m][flag] != -1)return dp[m][flag];
	int ret = 0;
	if (flag) { ret = dfs(m + 1, 0); dp[m][flag] = ret; }
	else { ret = max(dfs(m + 1, 0), dfs(m + 1, 1)+v[m]); dp[m][flag] = ret; }
	return ret;
}

int main() {
	cin >> n;
	rep(i, 0, n)cin >> v[i];
	memset(dp, -1, sizeof(dp));
	print(dfs(0, 0));
	return 0;
}