#include<stdio.h>  
    int v[1000000];  
    int main()  
    {  
		long long sum=0;
        int n,max,entr=0;  
        freopen("operatii.in","r",stdin);  
        freopen("operatii.out","w",stdout);  
        scanf("%d",&n);  
      int put=1;  
       for(int i=0;i<n;++i)  
       {  
           scanf("%d",v+i);
		max=0;
		   while(v[i])
			{
				if(max<v[i])
					max=v[i];
				++i;
			scanf("%d",v+i);
			if(!v[i])
				sum+=max;	
			}			
		   
	   }  
     printf("%lld",sum);  
       
     return 0;  
 }