#include <iostream>
#include <vector>
#include <algorithm>

void MinSupport(std::vector<int>& stack, std::vector<int>& min_stack, int num) {
    stack.push_back(num);
    if (min_stack.empty() || min_stack.back() > num) {
        min_stack.push_back(num);
    }
    else {
        min_stack.push_back(min_stack.back());
    }
}
void Queue(std::vector<int>& s_1, std::vector<int>& s_1_min, std::vector<int>& s_2, std::vector<int>& s_2_min, int num){
    if (num != 0) {
        MinSupport(s_1, s_1_min, num);
        return;
    }
    if (s_2.empty()) {
        if (s_1.empty()) {
            std::cout << -1  << std::endl;
            return;
        }
        for (auto n : s_1) {
            MinSupport(s_2, s_2, n);
        }
        s_1.clear();
        std::cout << s_2_min.back() << std::endl;
        s_2.pop_back();
        s_2_min.pop_back();
        return;
    }
    std::cout << std::min(s_1_min.back(), s_2_min.back()) << std::endl;
    s_2.pop_back();
    s_2_min.pop_back();
}
int main() {
    std::vector<int> s_1, s_1_min;
    std::vector<int> s_2, s_2_min;
    int operations_amount;
    std::cin >> operations_amount;
    for (int i = 0; i < operations_amount; ++i) {
        int num;
        std::cin >> num;
        Queue(s_1, s_1_min, s_2, s_2, num);
    }
    return 0;
}