Untitled

import java.util.Scanner;

public class MaximumMatrix {
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int T = scanner.nextInt(); // Number of test cases

        for (int t = 0; t < T; t++) {
            int n = scanner.nextInt(); // Number of rows
            int m = scanner.nextInt(); // Number of columns
            int K = scanner.nextInt(); // Maximum value for each cell
            int L = scanner.nextInt(); // Maximum sum of any pair of adjacent cells
            
            System.out.println(maximumSum(n, m, K, L));
        }
        
        scanner.close();
    }
    
    private static int maximumSum(int n, int m, int K, int L) {
        // Considering the constraints L >= 2 by setting the max allowable value in the matrix
        int maxAllowableValue = Math.min(K, L / 2);
        
        // Once the max allowable value is determined, fill the matrix with this value
        int sum = maxAllowableValue * n * m;

        return sum;
    }
}