#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

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

  vector<vector<int>> dp(n+1,vector<int>(2,0));
  dp[1][1] = v[0];
  for (int i = 1; i < n; i++){
    dp[i+1][0] = max(dp[i][1], dp[i-1][1]);
    dp[i+1][1] = max(dp[i][0] + v[i], dp[i-1][0] + v[i]);
  }
  cout << max(dp[n][0], dp[n][1]) << endl;
  return 0;
}