[BOJ] 28278 스택 2

#include <iostream>
#include <stack>
using namespace std;

int main() {
    int N;
    cin >> N;

    stack<int> s;

    for (int i = 0; i < N; i++) {
        int command;
        scanf("%d", &command);

        if (command == 1) {
            int X;

            scanf("%d", &X);

            s.push(X);
        } else if (command == 2) {
            if (!s.empty()) {
                printf("%d\n", s.top());
                s.pop();
            } else {
                printf("%d\n", -1);
            }
        } else if (command == 3) {
            printf("%d\n", s.size());
        } else if (command == 4) {
            printf("%d\n", (s.empty() ? 1 : 0));
        } else if (command == 5) {
            if (!s.empty()) {
                printf("%d\n", s.top());
            } else {
                printf("%d\n", -1);
            }
        }
    }

    return 0;
}