#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b, int mod=M) {
    int x = 1;
    a %= mod;
    while (b) {
        if (b & 1) x = (x * a) % mod; 
        a = (a * a) % mod;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************




vector<int> a;

int consistency(int n){
	
	vector<int> dpA(n);
	vector<int> dpB(n);
	vector<int> dpX(n);
	
	dpA[0] = max( 0LL, a[0]);
	dpB[0] = max( 0LL, a[0]);
	dpX[0] = 0;
	
	for(int i=1; i<n; i++){
		dpA[i] = a[i] + max( dpB[i-1] , dpX[i-1] );
		dpB[i] = a[i] + max( dpA[i-1] , dpX[i-1] );
		dpX[i] = max( { dpA[i-1] , dpB[i-1] , dpX[i-1] } );
	}
	
	return max( { dpA[n-1], dpB[n-1] , dpX[n-1] } );
}















int practice(int n){


    return 0;
}





void solve() {
    
    int n;
    cin>> n;
    
    a.resize(n);
    for(int i=0; i<n; i++) cin >> a[i];
    
    cout << consistency(n) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}