#include <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (int)n; ++i)
#define FOR(i, a, b) for(int i = a; i < (int)b; ++i)
#define rrep(i, n) for(int i = ((int)n - 1); i >= 0; --i)

typedef long long ll;
typedef long double ld;

const int Inf = 1e9;
const double EPS = 1e-9;
const int MOD = 1e9 + 7;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(0);
    int n;
    cin >> n;
    vector<int> v(n);
    rep (i, n) cin >> v[i];
    vector<int> dp(n + 1);
    dp[1] = v[0];
    FOR (i, 2, n + 1) {
        dp[i] = max(dp[i - 1], dp[i - 2] + v[i - 1]);
    }
    cout << dp[n] << endl;
    
    return 0;
}