#include <bits/stdc++.h>
#define FOR(i, begin, end) for(int i = (begin); i < (end); i++)
#define FAST_IO ios_base::sync_with_stdio(0); cin.tie(nullptr); cout.tie(nullptr)
#define f first
#define s second
#define pb push_back
#define sz(x) ((int)((x).size()))
#define le(vec) vec[vec.size()-1]
#define all(x) (x).begin(), (x).end()
#define TSTS int ttt; cin >> ttt; while(ttt--) solve()
using namespace std;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef pair<long double, long double> pdd;
typedef map<int, int> mii;
typedef vector<int> vi;
typedef long double ld;
typedef long long ll;
const int INF=1e9, MOD=1e9+7, mod=998244353;
const ll LINF=1e18;
void setIO()
{
FAST_IO;
}
void setIO(string s)
{
FAST_IO;
freopen((s+".in").c_str(), "r", stdin);
freopen((s+".out").c_str(), "w", stdout);
}
const int N=1e5+10;
int n, a[N], b[N];
vector<pii> inf;
vi ans;
bool can(int x, int y)
{
FOR(i, 2, n)
{
if(a[i]==x){
y-=b[i];
}
else if(a[i]==y){
x-=b[i];
}
else{
return false;
}
}
if(x==0 || y==0)
return true;
else
return false;
}
int main()
{
setIO();
cin >> n;
FOR(i, 0, n)
{
int aa, bb;
cin >> aa >> bb;
inf.pb({aa,bb});
}
sort(all(inf), greater<pii>());
FOR(i, 0, n)
{
a[i]=inf[i].f; b[i]=inf[i].s;
}
int x=a[1], y=a[0]-b[1];
if(can(x, y)){
ans.pb(min(a[1]+b[0], a[0]));
}
x=a[0]; y=a[1]-b[0];
if(can(x, y)){
ans.pb(min(a[1], a[0]+b[1]));
}
x=a[0]-a[1]; y=b[1];
if(can(x, y)){
ans.pb(min(a[0], b[0]+b[1]));
}
bool ok=true;
int sm=b[0];
FOR(i, 1, n)
{
if(a[i]!=sm && b[i]!=sm){
ok=false;
break;
}
}
if(ok) ans.pb(sm);
sort(all(ans));
cout << sz(ans) << "\n";
for(auto x : ans){
cout << x << "\n";
}
}
