#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <cstring>
#include <vector>
#include <algorithm>
#define MAX_N 1000

int main(){
  int* dp = (int*)malloc(MAX_N * sizeof(int));
  int n;
  int* v =(int*)malloc(MAX_N * sizeof(int));
  std::cin >> n;
  for(register int i = 0; i < n; i++){
    std::cin >> v[i];
  }
  for(register int i =0; i < n; i++){
    if(i <  2) dp[i] = v[i];
    else if(i == 2) dp[i] = v[i] + v[0];
    else dp[i] = std::max(dp[i -2],dp[i -3]) + v[i];
  }
  printf("%d\n",std::max(dp[n-1],dp[n-2]));
}