#include<fstream>

using namespace std;

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

int a[1000000];
void citire(int &n, int a[1000000])
{
     int i;
     fin>>n;
     for(i = 1; i <= n; i++)
     fin>>a[i];
}
int max(int x, int y,int a[1000000])
{
    int max = 0,i;
     for(i = x; i <= y; i++)
     if(a[i] > max)
     max = a[i];

return max;
}
void numarare(int n,int a[1000000])
{
     int i,p=0,x,y,j;
     for(i = 1; i <= n; i++)
     if(a[i] != 0)
     {
             x = i;
             for(j = i; j <= n+1; j++)
             if(a[j] == 0)
             {
                     y = j;
                     p+=max(x,y,a);
                     i = j;
                     break;
             }
             /*if(j == n)
             p+=max(x,n,a);*/
     }
     fout<<p;
}          
int main()
{
    int n;
    citire(n,a);
    numarare(n,a);
fin.close();
fout.close();

return 0;
}