#include <fstream>
using namespace std;

int n, i, j, m, nr, x, v[1000001], maxim[1000001];
char ok = 0;
long long s;

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

int main(){
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++){
        if(v[i] == 0)
            ok = 0;
        else
            if(ok == 0){
                nr++;
                ok = 1;
                maxim[nr] = v[i];
            }
            else
                if(v[i] > maxim[nr])
                    maxim[nr] = v[i];
    }
    for(i=1;i<=nr;i++)
        s += maxim[i];
    fout<<s;
    return 0;
}