#include <iostream>
#include <algorithm>

using namespace std;
const int N = 55;
int dp[N],a[N],n;
int maxn = -1; 

int main()
{
    scanf("%d",&n);
    for (int i = 1;i <= n;i++) scanf("%d",&a[i]);
    
    dp[1] = a[1];
    dp[2] = max(a[1],a[2]);
    
    maxn = max(dp[1],dp[2]);//与dp[1],dp[2]比较,更新maxn
    
    for (int i = 3;i <= n;i++) 
    {
        dp[i] = max(dp[i - 1],dp[i - 2] + a[i]);
        maxn = max(maxn,dp[i]);//与dp[1~n]比较,更新maxn
    }
    //for (int i = 1;i <= n;i++) printf("%d ",dp[i]);
    cout << maxn << endl;//maxn = dp[n]
    return 0;
}