#include <iostream>
#include <fstream>

using namespace std;

int n, i, j, v[1000005], rez, nr, mx;

int main()
{
    ifstream fin("operatii.in");
    ofstream fout("operatii.out");

    fin >> n;
    fin >> v[1];
    v[n+1] = 0;
    nr = 1;
    for (i = 2; i <= n+1; i++)
    {
        fin >> v[i];
        if (v[i] > mx)  mx = v[i];
        if (v[i]!= 0 && v[i-1]!= 0)
            nr++;
        else if (v[i] == 0 && v[i-1]!= 0)
        {
            rez += mx;
            mx = 0;
            nr = 1;
        }
        //cout << nr << " "<< mx << " " << rez << "\n";
    }
    fout << rez << "\n";
}
//0 2 2 1 0 1 2