import java.util.Stack;

public class Sample {

  public static void main(String[] args) {
    Stack<Integer> stack = new Stack<>();
    stack.push(1);
    stack.push(2);
    stack.push(3);

    int sum = 0;
    while (!stack.isEmpty()) {
      sum += stack.pop();
    }
    System.out.println(sum); // Stack 합계 구하기
    
    Stack<Integer> stack2 = new Stack<>();
    stack2.push(1);
    stack2.push(2);
    stack2.push(3);

    sum = stack2.stream().mapToInt(Integer::intValue).sum();
    System.out.println(sum); // Stream을 이용한 Stack 합계 구하기

  }
}