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

		if(crt==0||i==n)
		 {set=0; sol+=max; max=0;}
	}
	printf("%ld",sol);
	return 0;
}