#include <bits/stdc++.h>
using namespace std;

#define int long long

struct P{
	int x,y;
};

bool kuhn(vector<vector<int>>& g, vector<int>& b, int i) {
	vector<int> v(g.size());
	auto dfs = [&](auto self, int i) {
		if (v[i]) {
			return 0;
		}
		v[i] = 1;
		for (int j : g[i]) {
			if (b[j] == -2) {
				continue;
			}
			if (b[j] == -1 || self(self, b[j])) {
				b[j] = i;
				return 1;
			}
		}
		return 0;
	};
	return dfs(dfs, i);
}

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N;
	cin>>N;
	vector<P>v(N);
	for(int i=0;i<N;i++){
		cin>>v[i].x>>v[i].y;
	}
	int p=partition(v.begin(),v.end(),[&](P p){return p.x%2==p.y%2;})-v.begin();
	vector<vector<int>>g(p),gg(N-p);
	for(int i=0;i<p;i++){
		for(int j=p;j<N;j++){
			if(abs(v[j].x-v[i].x)+abs(v[j].y-v[i].y)==1){
				g[i].push_back(j-p);
				gg[j-p].push_back(i);
			}
		}
	}
	vector<int>b(N-p,-1),bb(p,-1);
	for(int i=0;i<p;i++){
		kuhn(g,b,i);
	}
	for(int i=0;i<N-p;i++){
		kuhn(gg,bb,i);
	}
	vector<int>ans;
	for(int i=0;i<N-p;i++){
		if(b[i]==-1){
			ans.push_back(p+i);
			continue;
		}
		int x=b[i];
		b[i]=-2;
		if(kuhn(g,b,x)){
			ans.push_back(p+i);
			b[i]=-1;
		}
		else{
			b[i]=x;
		}
	}
	for(int i=0;i<p;i++){
		if(bb[i]==-1){
			ans.push_back(i);
			continue;
		}
		int x=bb[i];
		bb[i]=-2;
		if(kuhn(gg,bb,x)){
			ans.push_back(i);
			bb[i]=-1;
		}
		else{
			bb[i]=x;
		}
	}
	cout<<ans.size()<<'\n';
	for(int i:ans){
		cout<<v[i].x<<' '<<v[i].y<<'\n';
	}
	return 0;
}