#include "bits/stdc++.h"
using namespace std;

#define mset(a,x) memset(a,x,sizeof(a))

int N;
vector<int> V;

int dp[1010][2];
int rec(int i, bool fetched) {
    int &r = dp[i][fetched];
    if (r != -1) return r;
    if (i == N) return r = 0;
    if (fetched)
        return r = rec(i + 1, 0);
    else
        return r = max(rec(i + 1, 1) + V[i], rec(i + 1, 0));
}

int main() {
    cin >> N; V.resize(N);
    for (int& v : V) cin >> v;
    mset(dp, -1);
    cout << rec(0, 0) << endl;
    return 0;
}