#include <stdio.h>

#define max(a, b) (a < b ? b : a)

int main(void)
{
	int N;
	int s1=0, s2=0, s3=0, a3=0;

	scanf("%d", &N);
	while (N--)
	{
		int s, a;
		scanf("%d", &a);
		s = max(max(s3, s2 + a), s1 + a3 + a);
		s1 = s2; s2 = s3; s3 = s;
		a3 = a;
	}
	printf("%d\n", s3);

	return 0;
}