#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N;
    cin >> N;
    vector<int>V(N),dp(N+2);
    rep(i,0,N)cin >> V[i];
    dp[0] = V[0];
    dp[1] = N == 1 ? V[0] : max(V[0],V[1]);
    rep(i,2,N){
        dp[i] = max(dp[i-2] + V[i], dp[i-1] ); 
    }
    cout << dp[N-1] << endl;
}