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

int v[MAX_N];
int dp[MAX_N];
int limit;

int sushi(int n, bool last){
 int val;
 if(limit <= n) return 0;
 else if(last == true) val =  sushi(n+1, false); 
 else val = std::max(sushi(n+1,false), sushi(n+1,true) + v[n]);
 return (dp[n] = val);
}

int main(){
 memset(dp,-1,sizeof(dp));
 std::cin >> limit;
 for(register int i = 0; i < limit; i++){
   std::cin >> v[i];
 }
 printf("%d\n",sushi(0,false));
}