#include <bits/stdc++.h>
#define F first
#define S second
//#define mp make_pair
#define pb push_back
#define loop(i,x,y) for(int i=x;i<=y;i++)

using namespace std;
typedef long long ll;

const int N = 5e3 + 9;
const int MOD = 1e9 + 7;
const int INF = 1e9 + 1;

int prefixSum[N], dp[N][N], A[N], prevOdd[N], nextOdd[N], segTree[2][N][4*N];

int main () {
    int n, firstOdd = -1, lastOdd = -1;
    cin >> n;

    for (int i = 1; i <= n; i++) {
        cin >> A[i];
        prefixSum[i] = prefixSum[i - 1] + A[i];
    }

    int last = 0;
    for (int i = 1; i <= n; i++) {
        if (last)
            prevOdd[i] = last;
        else prevOdd[i] = 0;

        if (A[i] & 1) {
            last = i;

            if (firstOdd == -1)
                firstOdd = i;
        }
    }

    last = 0;
    for (int i = n; i >= 1; i--) {
        if (last)
            nextOdd[i] = last;
        else nextOdd[i] = n + 1;

        if (A[i] & 1) {
            last = i;

            if (lastOdd == -1)
                lastOdd = i;
        }
    }

    dp[1][n] = prefixSum[n];

    for (int len = n - 1; len >= 1; len--) {
        for (int l = 1; l + len - 1 <= n; l++) {
            int r = l + len - 1;

            if (r >= lastOdd && l <= firstOdd) {
                dp[l][r] = prefixSum[r] - prefixSum[l - 1];

                continue;
            }

            int bestBelowFloor = -INF;

            if (r < lastOdd) {
                for (int k = nextOdd[r]; k <= nextOdd[nextOdd[r]] - 1; k++)
                    bestBelowFloor = max (bestBelowFloor, dp[l][k]);
            }

            if (l > firstOdd) {
                for (int k = prevOdd[prevOdd[l]] + 1; k <= prevOdd[l]; k++)
                    bestBelowFloor = max (bestBelowFloor, dp[k][r]);
            }

            dp[l][r] = prefixSum[r] - prefixSum[l - 1] + bestBelowFloor;
        }
    }

    int res = -INF;
    for (int l = 1; l <= n; l++) {
        int c = 0;
        for (int r = l; r <= n; r++) {
            if (A[r] & 1)
                c++;

            if (((prefixSum[r] - prefixSum[l - 1]) & 1) && c == 1)
                res = max (res, dp[l][r]);
        }
    }

    if (res == -INF)
        cout << -1 << "\n";
    else cout << res << "\n";

    return 0;
}