//In the name of 2002!
#include<iostream>
#include<vector>
#include<deque>
#include<set>
using namespace std;
const int MAX=1e6;
#define endl "\n"
vector<int> list[MAX];
vector<int> vertex;
int no_come[MAX];
deque<int> s;
vector<int> ans;
set<int> vs;

void topol(int e){
      int count=0;
      for(int i=0;i<vertex.size();i++){
            if(!no_come[vertex[i]])
                  s.push_back(vertex[i]);
      }
      while(s.size()){
            ans.push_back(s[0]);
            cout<<s[0]<<endl;
            for(int i=0;i<list[s[0]].size();i++){
                  if(s[0]!=list[s[0]][i]){
                        count++;
                        no_come[list[s[0]][i]]--;
                        if(no_come[list[s[0]][i]]==0)
                              s.push_back(list[s[0]][i]);
                  }
            } 
            s.pop_front();
      }
      if(count==e){
            for(int i=0;i<ans.size();i++)
                  cout<<ans[i]<<" ";
            cout<<endl;
      }
      else
            cout<<"Graph has not Topol"<<endl;
      
}

void input(){
      int e;
      cout<<"Please enter the number of edges:"<<endl;
      cin>>e;
      cout<<"Please enter the input and output vertices"<<endl;
      for(int i=0;i<e;i++){
            int v1,v2;
            cin>>v1>>v2;
            if(vs.find(v1)==vs.end()){
                  vs.insert(v1);
                  vertex.push_back(v1);
                  }
            if(vs.find(v2)==vs.end()){
                  vs.insert(v2);
                  vertex.push_back(v2);
                  }
            list[v1].push_back(v2);
            no_come[v2]++;
      }
      topol(e);
}

int main(){
      input();
      return 0;
}