import java.util.*;
 
class Ideone {
    public static void main(String[] args) {
        int[] a1 = {1, 5, 3, 21234};
        int[] a2 = {-4509, 200, 3, 40};
        int n = a1.length;
 
        int[] dp1 = new int[n];  // for a1
        int[] dp2 = new int[n];  // for a2
 
        dp1[0] = a1[0];
        dp2[0] = a2[0];
 
        if (n >= 2) {
            dp1[1] = Math.max(a1[1], dp1[0]);
            dp2[1] = Math.max(a2[1], dp2[0]);
        }
 
        for (int i = 2; i < n; i++) {
            dp1[i] = Math.max(dp1[i - 2], dp2[i - 2]) + a1[i];
            dp1[i] = Math.max(dp1[i], dp1[i - 1]);
 
            dp2[i] = Math.max(dp1[i - 2], dp2[i - 2]) + a2[i];
            dp2[i] = Math.max(dp2[i], dp2[i - 1]);
        }
 
        int ans = Math.max(dp1[n - 1], dp2[n - 1]);
        System.out.println(ans);
    }
}
 

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