#include <iostream>
#include <fstream>

using namespace std;

const int NM=1e6;

int n,ans;
int v[NM+2];

int main()
{
    ifstream f("operatii.in");
    ofstream g("operatii.out");
    f>>n;
    for(int i=1;i<=n;i++)
        f>>v[i];
    int i=1;
    while(i<=n)
    {
        if(v[i]==0)
        {
            i++;
            continue;
        }
        int vmax=0;
        while(v[i] && i<=n)
        {
            if(v[i]>vmax)
                vmax=v[i];
            i++;
        }
        ans+=vmax;
    }
    g<<ans<<'\n';
    f.close();
    g.close();
    return 0;
}