#include <iostream>
#include <bits/stdc++.h>
#include <utility>
using namespace std;
int main(){
int n; cin >> n;
vector<pair<int, int>> PossibleR;
for(int i = 0;i<n;i++){
int a, b; cin >> a >> b;
int CurrentPossibleRSize = static_cast<int>(PossibleR.size());
if(CurrentPossibleRSize==0){
PossibleR.push_back(make_pair(a,b));
continue;
}
vector<pair<int, int>> OtherPossibleR;
for(int x = 0;x < CurrentPossibleRSize;x++){
if(PossibleR.at(x).first==a){
OtherPossibleR.push_back(make_pair(a,PossibleR.at(x).second+b));
}
if(PossibleR.at(x).second==a){
OtherPossibleR.push_back(make_pair(PossibleR.at(x).first+b,a));
}
if(PossibleR.at(x).first==b){
OtherPossibleR.push_back(make_pair(b,PossibleR.at(x).second+a));
}
if(PossibleR.at(x).second==b){
OtherPossibleR.push_back(make_pair(PossibleR.at(x).first+a,b));
}
}
PossibleR = OtherPossibleR;
}
cout << PossibleR.size() << endl;
list<int> Output;
for(int i =0;i<static_cast<int>(PossibleR.size());i++){
Output.push_front(min(PossibleR.at(i).first,PossibleR.at(i).second));
}
Output.sort();
int LastNum = 0;
for(int i : Output){
if(LastNum==i){continue;};
LastNum = i;
cout << i << endl;
}
return 0;
}
