#include<bits/stdc++.h>
using namespace std;
ifstream fin("operatii.in");
ofstream fout("operatii.out");
int a[1000001],x,m,n,i,j,k,p1,p2,nr=0;
unsigned long long maxi=0;
int main()
{
 fin>>n;
  for(i=1;i<=n;i++)
   fin>>a[i];
 i=1;
 while(i<=n)
 {
   if(a[i]!=0)
   {j=i+1;maxi=a[i];
      while(a[j]!=0&&j<=n)
      {if(a[j]>maxi)
          maxi=a[j];
       j++;
      }
    nr=nr+maxi;
    i=j;
   }else
    i++;
 }
  fout<<nr;
}