#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];
    for (int i = 1; i < n; ++i) {
        dp[i] = std::max(dp[i - 1], a[i]);
        if (i - 2 >= 0) {
            dp[i] = std::max(dp[i], dp[i - 2] + a[i]);
        }
    }
    std::cout << dp[n - 1] << '\n';
    
    return 0;
}