#include <stdio.h>
#include <stdlib.h>
#define max(a, b) ((a) > (b) ? (a) : (b))
int main() {
    int n;
    scanf("%d", &n);
    int *v = (int *)malloc(sizeof(int) * (n + 1));
    int *dp = (int *)malloc(sizeof(int) * (n + 1));
    for (int i = 1; i != n + 1; i++) {
        scanf("%d", &v[i]);
    }
    dp[1] = v[1];
    for (int i = 2; i != n + 1; i++) {
        dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
    }
    printf("%d\n", dp[n]);

    system("pause");
    return 0;
}