#include<stdio.h>
int v[1000000];
int main()
{
	int nr=0,n,max=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);
		if(!v[i])
			if(!put)
				{nr+=max;put=1;max=0;}
		if(v[i]>max)
			{max=v[i];put=0;}
	}
	if(v[n-1])
		nr+=max;
	printf("%d",nr);
	
	return 0;
}