#include <iostream>
#include <queue>
using namespace std;
int main()


{

    queue <int> podr;
    string s;
    int n;
    cin>> s;
    while (s!="exit")
    {
        if (s=="push")
        {
            cin>>n;
            podr.push(n);
            cout<<"ok"<< endl;
        }
        if (s=="pop")
        {
             if (!podr.empty()) {
            cout<<podr.front()<<endl;
            podr.pop();
             }
             else cout<<"error"<<endl;
        }
        if (s=="front")
        {

            if (!podr.empty()) {

              cout<<podr.front()<<endl;

            }
            else
            cout<<"error"<<endl;
        }
        if (s=="size")
        {
            cout<<podr.size()<<endl;
        }
        if (s=="clear")
        {
        while(!podr.empty())
        {
            podr.pop();
        }
        cout<<"ok"<<endl;
        }






        cin>>s;
    }







    cout<<"bye";

    return 0;
}