#include <stdio.h>
int main()
{
	long long  n,i,max=0;  long long sol=0;
	int set=0;
	freopen("operatii.in","r",stdin);
	freopen("operatii.out","w",stdout);
	scanf("%ld",&n);
	long long crt=0;
	for(i=1;i<=n;i++)
	{
		scanf("%lld",&crt);
		if(crt!=0)
		 set=1;
		if(set)
		{
			if(crt>max)
			   {	max=crt; }
		}
		if(i==n||crt==0)
		{	sol+=max; max=0; }

		if(crt==0)
		 {set=0;  max=0;}
	}
	printf("%lld",sol);
	return 0;
}