#include<stdio.h>

int main(void) {
	int N;
	int V[1001];
	long long int a[1001];

	scanf("%d", &N);
	for (int i = 1; i <= N; i++) {
		scanf("%d", &V[i]);
	}

	a[1] = V[1];
	if (V[1] < V[2]) a[2] = V[2];
	else a[2] = V[1];

	for (int i = 3; i <= N; i++) {
		if (V[i] + a[i - 2] > a[i - 1]) {
			a[i] = V[i] + a[i - 2];
		}
		else a[i] = a[i - 1];
	}

	printf("%d", a[N]);

	return 0;
	
}