#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
int N;
int max(int a,int b){
  return a>b ? a : b;
}
int saiki(int* v,int n,int temp){
  if(n<N){
    return max(saiki(v,n+1,temp),saiki(v,n+2,temp+v[n]));
  }else
    return temp;
}
int main(void){
int i;
scanf("%d",&N);
int v[N];
for(i=0;i<N;i++)
  scanf("%d",&v[i]);
printf("%d\n",saiki(v,0,0));
  return 0;
}