#include <stdio.h>
#include <stdlib.h>

int main(void)
{
	short n,i,*score;
	char *v;
	int ans;

	scanf("%hd",&n);
	v = (char *)malloc(sizeof(char) * n);
	if (v == NULL) {
		perror("v malloc");
		exit(1);
	}
	for (i=0;i<n;i++) scanf("%hhd",&v[i]);

	score = (short *)malloc(sizeof(short) * n);
	score[0] = v[0];
	if (n > 1) score[1] = (score[0] > v[1])? score[0]:v[1];
	for (i=2;i<n;i++) {
		if (score[i-1] > score[i-2]+v[i]) {
			score[i] = score[i-1];
		} else {
			score[i] = score[i-2]+v[i];
		}
	}
	ans = score[n-1];

	printf("%d\n",ans);

	return 0;
}