#include <stdio.h>
int p[10001];
int dp[10001];
int get_max(int a, int b) {
return a > b ? a : b;
}
int main() {
//freopen("input.txt", "rt", stdin);
int n;
scanf("%d", &n);
for (int i = 1; i <= n; i++) {
scanf("%d", &p[i]);
}
dp[0] = 0;
dp[1] = p[1];
dp[2] = p[1] + p[2];
int m = 0;
for (int i = 3; i <= n; i++) {
dp[i] = get_max(dp[i - 1], get_max(dp[i - 2] + p[i], dp[i - 3] + p[i - 1] + p[i]));
}
printf("%d", dp[n]);
return 0;
}