#include <iostream>
#include <fstream>
using namespace std;

ifstream in("operatii.in");
ofstream out("operatii.out");

const int N_max = 1000005;

int v[N_max];

bool viz[N_max];

long long ans;

int N;

int main()
{
    int i;

    in >> N;

    for(i = 1; i <= N; i++) in >> v[i];

    for(i = 1; i <= N; i++)
        if(!v[i]) viz[i] = true;

    viz[0] = viz[N + 1] = true;

    int Max = -1;

    for(i = 0; i <= N + 1; i++)
    {
        if(v[i]) Max = max(Max, v[i]);

        if(!v[i])
        {
            //cout << Max << '\n';

            if(Max > 0) ans += Max;

            Max = 0;
        }
    }

    out << ans;

    return 0;
}