#include <bits/stdc++.h>
#include <atcoder/all>


using namespace std;
using namespace atcoder;
#define rep(i,m,n,k) for (int i = (int)(m); i < (int)(n); i += (int)(k))
#define rrep(i,m,n,k) for (int i = (int)(m); i > (int)(n); i += (int)(k))
#define ll long long
#define list(T,A,N) vector<T> A(N);for(int i=0;i<(int)(N);i++){cin >> A[i];}


int main(){
    
    ll N;
    cin >> N;
    list(ll,V,N);
    vector<vector<ll>> dp(2,vector<ll>(N,-1));
    ll v0 = V[0];
    dp[0][0] = 0;
    dp[1][0] = v0;
    ll v;
    rep(i,0,N-1,1){
        v = V[i+1];
        dp[0][i+1] = max(dp[0][i],dp[1][i]);
        dp[1][i+1] = dp[0][i] + v;
    }
    cout << max(dp[0][N-1],dp[1][N-1]) << endl;
    return 0;
}