#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    int v[n];
    rep(i,n)cin >> v[i];

    int dp[n][2];

    rep(i,n){
        if(i == 0){
            dp[i][0] = 0;
            dp[i][1] = v[i];
        }else{
            dp[i][0] = max(dp[i-1][0], dp[i-1][1]);
            dp[i][1] = dp[i-1][0] + v[i];
        }
    }
    cout << max(dp[n-1][0], dp[n-1][1]) << endl;
    return 0;
}