#include<cstdio>
int main()
{
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    int n;
    scanf("%d",&n);
    int i=0;
    int x;
    for(;i<n;++i)
    {
        scanf("%d ",&x);
        if(x)
            break;
    }
    int max=x,s=0;
    for(;i<n;++i)
    {
        scanf("%d ",&x);
        if(x)
        {
            if(x>max)
                max=x;
        }
        else
            s+=max,max=0;
    }
    s+=max;
    printf("%d\n",s);
    return 0;
}