D.cpp

//#pragma GCC optimize "trapv"
#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3", "unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include<bits/stdc++.h>
#define ll long long int
#define fab(a,b,i) for(int i=a;i<b;i++)
#define pb push_back
#define db double
#define mp make_pair
#define endl "\n"
#define f first
#define se second
#define all(x) x.begin(),x.end()
#define MOD 1000000007
#define vll vector<ll>
#define vi vector<int>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define quick ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
ll add(ll x, ll y) {ll res = x + y; return (res >= MOD ? res - MOD : res);}
ll mul(ll x, ll y) {ll res = x * y; return (res >= MOD ? res % MOD : res);}
ll sub(ll x, ll y) {ll res = x - y; return (res < 0 ? res + MOD : res);}
ll power(ll x, ll y) {ll res = 1; x %= MOD; while (y) {if (y & 1)res = mul(res, x); y >>= 1; x = mul(x, x);} return res;}
ll mod_inv(ll x) {return power(x, MOD - 2);}

using namespace std;
const int N=1e3+3;
vector<int> v[N];
int par[N];
vector< pair<int,int> > getrid;
void dfs( int src, int parent, bool vis[])
{
	vis[src]=1;
	par[src]=par[parent];
	for(auto i: v[src])
	{
		if(i^parent)
		{
			if(!vis[i])
				dfs(i,src,vis);
			else
			{
				 if(i<src)
				getrid.pb({i,src});
			}
		}
	}
}

int main()
{ quick;
#ifndef ONLINE_JUDGE
    freopen("D:/sublime/input.txt", "r", stdin);
    freopen("D:/sublime/output.txt", "w", stdout);
#endif
	int n;
	cin>>n;
	fab(0,n-1,i)
	{
		int x,y;
		cin>>x>>y;
		x--;
		y--;
		v[x].pb(y);
		v[y].pb(x);
	}

	bool vis[n]={0};
	int cnt=0;
	fab(0,n,i)
	{
		if(!vis[i])
		{
			par[i]=i;
			dfs(i,i,vis);
			cnt++;
		}

	}
	vector<int> set_leaders;
	fab(0,n,i)
	{
		if(par[i]==i)
		{
			set_leaders.pb(i);
		}

	}
	cout<<cnt-1<<endl;
	// for(auto i: getrid)
	// {
	// 	cout<<i.f<<" "<<i.se<<endl;
	// }
	assert(getrid.size()==cnt-1);
	fab(0,cnt-1,i)
	{
		auto j=getrid.back();
		getrid.pop_back();
		cout<<j.f+1<<" "<<j.se+1<<" "<<set_leaders.back()+1<<" "<<set_leaders[0]+1<<endl;
		set_leaders.pop_back();
	}
	

 cerr << "time taken : " << (float)clock() / CLOCKS_PER_SEC << " secs" << endl;
	return 0;
}