#include <bits/stdc++.h>

using i64 = long long;

int main() {

    std::cin.tie(nullptr)->sync_with_stdio(false);

    int n;
    std::cin >> n;

    std::vector<i64> a(n);

    for (auto &x : a) std::cin >> x;

    constexpr i64 inf = std::numeric_limits<i64>::max() >> 4;

    std::vector<i64> dp(n, -inf);

    dp[0] = a[0];
    i64 max = -inf;
    for (int i = 1; i < n; ++i) {
        dp[i] = a[i];
        if (i - 2 >= 0) {
            max = std::max(max, dp[i - 2]);
            dp[i] = std::max(dp[i], dp[i] + max);
        }
    }

    std::cout << dp[n - 1] << '\n';

    return 0;
}