Intro: Buggy Loop

Identify the bug in the below loop (and fix it if you want!)

module counter_checker;
  logic [3:0] values[0:3]; // Array of 4 elements
  int sum = 0;

  initial begin
    // Initialize array
    values[0] = 1;
    values[1] = 2;
    values[2] = 3;
    values[3] = 4;

    // Buggy loop: supposed to sum all 4 elements
    for (int i = 0; i < 3; i++) begin
      sum += values[i];
    end
    $display("Sum is: %0d", sum); // Expected: 10, Actual: 6
  end
endmodule