import java.util.*;
import java.io.*;
import static java.lang.Math.*;

public class Main {

    private static final int MOD = (int)1e9 + 7; //998244353;
    private static final long INF = (long)1e15;

    public Main(FastScanner in, PrintWriter out) {
        int N = in.nextInt();
        int[] A = new int[N];
        for (int i = 0; i < N; i++)
            A[i] = in.nextInt();
		// j is the number of items took
        // dp[i][0] => j = floor(i / 2) - 1
        // dp[i][1] => j = floor(i / 2)
        // dp[i][2] => j = floor(i / 2) + 1
        long[][] dp = new long[N + 1][3];
        for (long[] r : dp)
            Arrays.fill(r, -INF);
        dp[0][1] = 0; // j = 0 // take 0 item
        dp[1][2] = A[0]; // j = 1 -- take 1st item

        for (int i = 1; i <= N; i++) {
            for (int j = 0; j < 3; j++) {
                if (i > 1) {
                    dp[i][j] = dp[i - 2][j] + A[i - 1];
                }
                if ((i & 1) == 1) {
                    dp[i][j] = Math.max(dp[i][j], dp[i - 1][j]);
                } else if (j < 2) {
                    dp[i][j] = Math.max(dp[i][j], dp[i - 1][j + 1]);
                }
            }
        }
        out.println(dp[N][1]);
    }

    private Map<Long, Long> memo;
    private long go(int[] A, long i, long j) {
        long N = A.length;
        if (i >= N) {
            if (j == 0) return 0;
            else return -INF;
        }
        // long k = N / 2 - j;
        // if (k < i / 2 - 1 || k > (i + 1) / 2)
            // return -INF;
        if (j > (N - i + 1) / 2 || j < (N - i) / 2 - 1)
            return -INF;
        long key = (i << 32) | j;
        if (memo.containsKey(key))
            return memo.get(key);

        long res = go(A, i + 1, j);
        res = Math.max(res, go(A, i + 2, j - 1) + A[(int)i]);
        memo.put(key, res);
        return res;
    }

    private int gcd(int a, int b) {
        while (true) {
            if (b == 0) return a;
            int tmp = a;
            a = b;
            b = tmp % b;
        }
    }

    private long pow(long x, long p) {
        long res = 1;
        while (p > 0) {
            if (p % 2 == 1)
                res = res * x % MOD;
            x = x * x % MOD;
            p /= 2;
        }
        return res;
    }

    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        // Scanner in = new Scanner(
                // new BufferedReader(new InputStreamReader(System.in)));
        FastScanner in = new FastScanner(System.in);

        Main sol = new Main(in, out);

        out.close();
    }
}

// Pair
class Pair<T extends Comparable<? super T>, U extends Comparable<? super U>> implements Comparable<Pair<T, U>> {
    T a;
    U b;
    Pair() { }
    Pair(T a, U b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public String toString() { return "("+a.toString()+", "+b.toString()+")"; }

    @Override
    public int hashCode() { return Objects.hash(a, b); }

    @Override
    public boolean equals(Object obj) {
        if(this == obj) return true;
        if(obj == null) return false;
        if(this.getClass() != obj.getClass()) return false;
        Pair that = (Pair) obj;
        if(this.a.getClass() != that.a.getClass()) return false;
        if(this.b.getClass() != that.b.getClass()) return false;
        if(!this.a.equals(that.a)) return false;
        if(!this.b.equals(that.b)) return false;
        return true;
    }

    @Override
    public int compareTo(Pair<T, U> that) {
        int c = (this.a).compareTo(that.a);
        if(c == 0) c = (this.b).compareTo(that.b);
        return c;
    }
}


class FastScanner{
    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;

    public FastScanner(InputStream stream)
    {
        this.stream = stream;
    }

    int read()
    {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars){
            curChar = 0;
            try{
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }

    boolean isSpaceChar(int c)
    {
        return c==' '||c=='\n'||c=='\r'||c=='\t'||c==-1;
    }

    boolean isEndline(int c)
    {
        return c=='\n'||c=='\r'||c==-1;
    }

    int nextInt()
    {
        return Integer.parseInt(next());
    }

    long nextLong()
    {
        return Long.parseLong(next());
    }

    double nextDouble()
    {
        return Double.parseDouble(next());
    }

    String next(){
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isSpaceChar(c));
        return res.toString();
    }

    String nextLine(){
        int c = read();
        while (isEndline(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isEndline(c));
        return res.toString();
    }
}


Measured memory_bytes: 53544