#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) FOR(i,0,n)
#define repr(i,n) for(int i=(n)-1;0<=i;--i)
#define each(e,v) for(auto&& e:(v))
#define all(v) begin(v),end(v)
#define DUMP(x) cerr<<#x<<": "<<(x)<<endl
#define DEBUG(x) cerr<<#x<<": "<<(x)<<" (L"<<__LINE__<<")"<<endl
using namespace std;
using vint = vector<int>;
using vdouble = vector<double>;
using vstring = vector<string>;
using ll = long long;
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }

vint v, memo;

int dfs(int i) {
    if(i < 0) return 0;
    if(memo[i] >= 0) return memo[i];
    if(i == 0) return v[0];
    memo[i] = max(dfs(i-2), dfs(i-3)) + v[i];
    return memo[i];
}

int main() {
    int n; cin >> n;
    v = vint(n); memo = vint(n, -1);
    rep(i, n) cin >> v[i];
    cout << dfs(n-1) << endl;
    return 0;
}