include <iostream>

include <deque>

using namespace std; int main() { deque<int>v; string s; int n,k; while(1) { cin>>s; if(s=="push") { cin>>n; v.push_back(n); cout<<"ok"<<endl; } else if(s=="pop") { if(!v.empty()){ cout<<v.front()<<endl; v.pop_front(); } else{ cout<<"error"<<endl; } } else if(s=="front") { if(!v.empty()) cout<<v.front()<<endl; else cout<<"error"<<endl; } else if(s=="size") { cout<<v.size()<<endl; } else if(s=="clear") { cout<<"ok"<<endl; v.clear(); } else if(s=="exit") { cout<<"bye"<<endl; return 0; }

}

}

include<bits/stdc++.h>

using namespace std; int main(){ queue<int> q; int d; string a; while(cin>>a and a!="exit"){ if(a=="push"){ cin>>d; q.push(d); cout<<"ok\n"; } if(a=="pop"){ if(q.empty()) cout<<"error\n"; else{ cout<<q.front()<<'\n'; q.pop();} } if(a=="front"){ if(q.empty()) cout<<"error\n"; else cout<<q.front()<<'\n';} if(a=="size") cout<<(int)q.size()<<'\n'; if(a=="clear"){ while(!q.empty()) q.pop(); cout<<"ok\n"; } } cout<<"bye"; return 0; }