#include<bits/stdc++.h>
#define pb push_back
#define int long long
#define vi vector<int>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define vpii vector<pair<int, int>>
#define vc vector<char>
#define vb vector<bool>
#define mii map<int,int>
#define f0r(i,n) for(int i=0;i<n;i++)
#define FOR(i,k,n) for(int i=k;i<n;i++)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define in(a) int a; cin>>a
#define in2(a,b) int a,b; cin>>a>>b
#define in3(a,b,c) int a,b,c; cin>>a>>b>>c
#define in4(a,b,c,d) int a,b,c,d; cin>>a>>b>>c>>d
#define vin(v,n); vi v(n); f0r(i,n){cin>>v[i];}
#define out(a) cout<<a<<'\n'
#define out2(a,b) cout<<a<<' '<<b<<'\n'
#define out3(a,b,c) cout<<a<<' '<<b<<' '<<c<<'\n'
#define out4(a,b,c,d) cout<<a<<' '<<b<<' '<<c<<' '<<d<<'\n'
#define vout(v) for(auto u : v){cout<<u<<' ';} cout<<'\n'
#define dout(a) cout<<a<<' '<<#a<<'\n'
#define dout2(a,b) cout<<a<<' '<<#a<<' '<<b<<' '<<#b<<'\n'
#define yn(x); if(x){cout<<"YES"<<'\n';}else{cout<<"NO"<<'\n';}
const int leg = 1e9 + 7;
const int mod = 998244353;
using namespace std;
signed main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
//ifstream cin(".in");
//ofstream cout(".out");
in(n);
vpii v;
f0r(i,n){
in2(a,b);
v.pb({a,b});
}
if(n <= 10){
set<int>s;
do{
vpii curr = {v[0]};
bool ok = 1;
FOR(i, 1, n){
vpii c;
for(auto cur : curr){
if(cur.first == v[i].first && cur.second == v[i].second){
int a = cur.first * 2;
int b = cur.second;
if(a < b)swap(a,b);
c.pb({a,b});
a = cur.second * 2;
b = cur.first;
if(a < b)swap(a,b);
c.pb({a,b});
}
else if(cur.first == v[i].second){
int a = cur.first;
int b = cur.second + v[i].first;
if(a < b)swap(a,b);
c.pb({a,b});
}
else if(cur.second == v[i].first){
int a = cur.second;
int b = cur.first + v[i].second;
if(a < b)swap(a,b);
c.pb({a,b});
}
else if(cur.first == v[i].first){
int a = cur.first;
int b = cur.second + v[i].second;
if(a < b)swap(a,b);
c.pb({a,b});
}
else if(cur.second == v[i].second){
int a = cur.second;
int b = cur.first + v[i].first;
if(a < b)swap(a,b);
c.pb({a,b});
}
}
curr = c;
}
for(auto u : curr){
s.insert(u.second);
}
}while(next_permutation(all(v)));
out(s.size());
for(auto u : s)out(u);
}
else{
vi w;
vi ans;
f0r(i, n){
w.pb(v[i].first);
}
set<int>s;
f0r(i,n)s.insert(w[i]);
int sum = 0;
f0r(i, n)sum += w[i];
FOR(i, 1 , n+1){
if(sum % i == 0 && sum / i >= i){
if(i == 1){
ans.pb(i);
}
else{
int l = sum / i;
bool ok = 1;
int tmp = 0;
tmp += l;
if(s.count(l) == 0)ok = 0;
for(int j = i-1; j>=2; j--){
l--;
if(s.count(j) == 0 || s.count(l) == 0){
ok = 0;
}
tmp += l;
tmp += j;
}
if(ok){
if(sum == tmp + l || sum == tmp + l + i){
ans.pb(i);
}
}
}
}
}
}
}
