#include <iostream>
#include <string>
#include <set>
#include <map>
#include <vector>
#include <numeric>
#include <tuple>
#include <cstdio>

using namespace std;

typedef long long ll;


#define rep(i,b) for(ll i=0;i<(b);++i)
#define rep1(i,b) for(ll i=1;i<=(b);++i)
#define vec vector
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl;

int N;
ll dp[1100];
ll V[1100];

ll rec(int i) {
   if (i > N) {
      return 0;
   }
   if (dp[i] < 0) {
      dp[i] = max(rec(i+2)+V[i], rec(i+1));
   }
   return dp[i];
}

int main() {
   cin >> N;
   rep(i, N) {
      cin >> V[i];
   }
   rep(i, 1100) {
      dp[i] = -1;
   }
   cout << rec(0) << endl;
}