#include<stdio.h>
unsigned long n,i,nr,max,rez;

void citire()
{freopen("operatii.in","r",stdin);
scanf("%ul",&n);


for(i=1;i<=n;i++)
 {scanf("%ul",&nr);
   if(nr==0)
    {rez=rez+max;
     max=0;
    }
   else
    {if(nr>max)
      max=nr;
    }
 }
 rez=rez+max;
fclose(stdin);
}

void afisare()
{freopen("operatii.out","w",stdout);
printf("%u", rez);
fclose(stdout);
}

int main()
{citire();
afisare();
return 0;
}