import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class Main {
    static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

    public static void main(String[] args) {
        try {
            IRunner runner = new Runner(br, bw);
            runner.run();
            runner.flush();

            br.close();
            bw.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

class Runner implements IRunner {
    final IReader reader;
    final BufferedWriter bw;
    final StringBuilder sb = new StringBuilder();

    final int N;
    final int[] values;
    final int[][] scores;

    Runner(BufferedReader br, BufferedWriter bw) {
        this.reader = new Reader(br);
        this.bw = bw;

        try {
            var input = reader.readInts();
            N = input[0];
            values = reader.lines()
                    .mapToInt(Integer::parseInt)
                    .toArray();
            scores = new int[N][2];
            sb.ensureCapacity(20);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void flush() {
        try {
            bw.write(sb.toString());
            bw.flush();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void run() throws IOException {
        scores[0][0] = values[0];
        if (N > 1) {
            scores[1][0] = values[1];
            scores[1][1] = values[0] + values[1];
        }

        // 단순 점화식은
        // f(x) = max( arr[x] + f(x-1), arr[x] + f(x-2) )
        // 하지만 연속된 3개의 계단을 밟는 결과가 나와서는 안 됨
        // 따라서 각 위치에 대한 dp 값은 연속으로 참조한 계단의 수가 포함되어야 함

        for (int i = 0; i < N; i++) {
            forward(i, 1);
            forward(i, 2);
        }
        sb.append(Math.max(scores[N - 1][0], scores[N - 1][1])).append('\n');
    }

    void forward(int iFrom, int step) {
        if (iFrom + step >= N) {
            return;
        }

        int next = values[iFrom + step];
        int prev = 0;

        if (step == 1) {
            prev = scores[iFrom][0];
            scores[iFrom + step][1] = Math.max(scores[iFrom + step][1], prev + next);
        } else if (step == 2) {
            prev = Math.max(scores[iFrom][0], scores[iFrom][1]);
            scores[iFrom + step][0] = Math.max(scores[iFrom + step][0], prev + next);
        }
    }
}

class Reader implements IReader {
    private BufferedReader br;

    public Reader(BufferedReader br) {
        this.br = br;
    }

    @Override
    public void skipLine() throws IOException {
        br.readLine();
    }

    @Override
    public Stream<String> lines() throws IOException {
        return br.lines();
    }

    @Override
    public String line() throws IOException {
        return br.readLine();
    }

    @Override
    public int[] readInts() throws IOException {
        String[] tokens = br.readLine().split(" ");
        int[] ints = new int[tokens.length];
        for (int i = 0; i < tokens.length; ++i) {
            ints[i] = Integer.parseInt(tokens[i]);
        }
        return ints;
    }

    @Override
    public List<Integer> readIntegers() throws IOException {
        String[] tokens = br.readLine().split(" ");
        var res = new ArrayList<Integer>(tokens.length);
        for (String token : tokens) {
            res.add(Integer.valueOf(token));
        }
        return res;
    }
}

interface IRunner {
    void run() throws IOException;

    void flush();
}

interface IReader {
    void skipLine() throws IOException;

    Stream<String> lines() throws IOException;

    String line() throws IOException;

    List<Integer> readIntegers() throws IOException;

    int[] readInts() throws IOException;
}