#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(set==1&&crt==0)
		{ sol+=max; max=0; set=0;}
		else
		if(crt!=0)
		{       set=1;
			if(crt>max) max=crt;
		}
		if(i==n)
		  sol+=max;
	}
	printf("%lld",sol);
	return 0;
}