#include <stdio.h>
#define Nmax 100001

int c[Nmax];

int n, i, rez;
int v[Nmax];
inline int max(int x, int y) { return x > y ? x : y; }

int main()
{
	freopen("oo.in", "r", stdin);
	scanf("%d ", &n);
	for (i=1; i<=n; i++)
		scanf("%d ", &v[i]);
	fclose(stdin);

	c[2] = rez = v[2] + v[1];

	for (i = 5; i<n; i++)
	{
		c[i] = v[i] + v[i-1] + max(c[i-5], c[i-4]);
		rez = max(rez,c[i]);
	}

	c[2] = c[5] = 0;
	c[3] = v[3] + v[2];
	rez = max(rez, c[3]);

	for (i = 6; i<=n; i++)
	{
		c[i] = v[i] + v[i-1] + max(c[i-5], c[i-4]);
		rez = max(rez, c[i]);
	}

	fprintf(fopen("oo.out", "w"), "%d ", rez);
	return 0;
}