#include <cstdio>
using namespace std;
int v[1000001];
int main()
{
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    int max=0,ok,n,i,s=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);
        if(v[i]>max)
            max=v[i];
        if(v[i]==0)
            {
            s+=max;
            max=0;
            }
    }
    if(max>0)
    s+=max;
    printf("%d",s);
}