删一个之后还剩几个没归还

运行下面这段程序：

#include <iostream>
#include <string>
#include <vector>
using namespace std;

struct Node {
    string name;
    Node* next = nullptr;
};

int alive = 0;   // 现在还有几个节点没有归还

Node* make(const string& name) {
    alive++;
    return new Node{name};
}

void drop(Node* nd) {
    alive--;
    delete nd;
}

Node* build(const vector<string>& names) {
    Node* head = nullptr;
    for (int i = (int)names.size() - 1; i >= 0; i--) {
        Node* nd = make(names[i]);
        nd->next = head;
        head = nd;
    }
    return head;
}

int main() {
    Node* head = build({"阿岚", "小满", "阿泰", "南风"});
    Node* gone = head->next;
    head->next = gone->next;
    drop(gone);
    cout << alive << endl;
}

（本题用 g++ -std=c++17 -O0 编译。）