#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include<math.h>
#define swap(type,a,b) do{type t=a;a=b;b=t;}while(0);
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))
#define ll long long
#define INF 100000000
#define FOR(i,a,n) for(i=a;i<n;i++)
void fill(int a[],int b,int c){
	int i;
	FOR(i,0,b) a[i]=c;
	return;
}
int v[1000];
int dp[1001];
int main(void)
{
    int n,i;
    scanf("%d",&n);
    FOR(i,0,n) scanf("%d",&v[i]);
    dp[0]=0,dp[1]=v[0];
    FOR(i,2,n+1) dp[i]=MAX(dp[i-1],dp[i-2]+v[i-1]);
    printf("%d\n",dp[n]);
 	return 0;
}