#include <cstdlib>

#include <iostream>

#include <map>

#include <queue>

#include <sstream>

#include <string>

#include <unordered_map>

#include <unordered_set>

#include <vector>

using namespace std;

class ZigzagIterator {

int current_it;

int it1;

int it2;

vector<int> vec1;

vector<int> vec2;

public:

ZigzagIterator(vector<int>& v1, vector<int>& v2) {

current_it = 1;

it1 = 0;

it2 = 0;

vec1 = v1;

vec2 = v2;

}

int next() {

if (current_it == 1) {

current_it = 2;

if (it1 < vec1.size()) {

it1++;

return vec1[it1 - 1];

}

}

// else

current_it = 1;

it2++;

return vec2[it2 - 1];

}

bool hasNext() {

return it1 < vec1.size() || it2 < vec2.size();

}

};

int main() {

vector<int> v1 = {1, 2};

vector<int> v2 = {3, 4, 5, 6};

ZigzagIterator i(v1, v2);

while (i.hasNext()) {

cout << i.next();

}

return 0;

}