#include <algorithm>
#include <iostream>
#include <iomanip>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

#define FOR(i,s,e) for (int i = int(s); i != int(e); i++)
#define FORIT(i,c) for (typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define ISEQ(c) (c).begin(), (c).end()

int main(){
    int N;
    cin >> N;

    int V[N];
    FOR(i,0,N) cin >>V[i];

    int mV[N];
    mV[0] =  V[0];
    if(N == 0){
        cout << mV[0] << endl;
        return 0;
    }

    mV[1] = max(V[0],V[1]);
    if(N == 1){
        cout << mV[1] << endl;
        return 0;
    }

    FOR(i,2,N){
    	int max =  -1;
    	FOR(j,0,i-1){
    		if (V[i] + mV[j] > max) max = V[i] + mV[j];
    	}
    	if (max < mV[i-1]) max = mV[i-1];
    	mV[i] = max;
    }

    cout << mV[N-1] << endl;
    return 0;
}