#include <fstream>

#define input "operatii.in"
#define output "operatii.out"
#define NMAX 1000005

using namespace std;

ifstream in(input);
ofstream out(output);

int N, sir[NMAX];

void Read_Data()
{
    in >> N;
    for(int i = 1; i <= N; i++)
        in >> sir[i];
}

void Solve()
{
    int sol = 0;
    for(int i = 1; i <= N; i++)
    {
        while(sir[i] == 0 && i <= N) i++;
        // Incepem de pe pozitia i
        int maxim = sir[i];
        while(sir[i] != 0 && i <= N)
        {
            maxim = max(maxim, sir[i]);
            i++;
        }
        sol += maxim;
    }
    out << sol << "\n";
}

int main()
{
    Read_Data();
    Solve();
    return 0;
}