import java.util.*;
 
class Ideone {
    public static void main(String[] args) throws java.lang.Exception {
        Scanner sc = new Scanner(System.in);
        int n = 5; // Size of the array
        int[] arr = new int[n]; // Initialize the array
 
        // Input array elements
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
 
        int b = sc.nextInt(); // Read the number of selections allowed
 
        // If the number of selections exceeds half the array size, return -1
        if (b > (n / 2) + 1) {
            System.out.print(-1);
            return;
        }
 
        int left = 0; // Pointer for the left side of the array
        int right = n - 1; // Pointer for the right side of the array
        int sum = 0; // Variable to store the sum
 
        // While we have selections left
        while (b > 0) {
            // Compare the leftmost and rightmost elements
            if (arr[left] > arr[right]) {
                sum += arr[left]; // Take the left element
                left++; // Move the left pointer to the right
            } else {
                sum += arr[right]; // Take the right element
                right--; // Move the right pointer to the left
            }
            b--; // Decrease the number of selections left
        }
 
        System.out.print(sum); // Output the maximum sum
    }
}
 

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NiAtMiAzIDQgNQozCg==

6 -2 3 4 5
3