package baekjoon.DP;
import java.util.*;
import java.io.*;
class Main2156 {
static int[] D, A;
public static void main(String[] args) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st;
int N = Integer.parseInt(br.readLine());
D = new int[N + 1];
A = new int[N + 1];
for (int i = 1; i <= N; i++) {
A[i] = Integer.parseInt(br.readLine());
}
// D[N] = max(D[N-1], (D[N-2]+A[N]) , (D[N-3] + +A[i-1] + A[N])
if (N >= 1)
D[1] = A[1];
if (N >= 2)
D[2] = D[1] + A[2];
if (N >= 3)
D[3] = Math.max(D[2], Math.max(D[1] + A[3], A[1] + A[3]));
for (int i = 4; i <= N; i++) {
D[i] = Math.max(D[i - 1], Math.max(D[i - 2], D[i - 3] + A[i - 1]) + A[i]);
}
System.out.println(D[N]);
}
}
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