#include <bits/stdc++.h>

using namespace std;

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

const double PI = acos(-1);

int n;
int v[1010];
int dp[1010];

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

  cin >> n;
  REP (i, n) cin >> v[i+1];
  
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    int base = i-2 >= 0 ? dp[i-2] : 0;
    dp[i] = max(dp[i-1], v[i] + base);
  }

  cout << dp[n] << endl;
  
  return 0;
}