#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using vl = vector<ll>;
#define rep(i,n) for(int i=0;i<(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define fore(i_in,a) for (auto& i_in: a)
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define fio() cin.tie(nullptr);ios::sync_with_stdio(false);
#define DEBUG_CTN(v) cerr<<#v<<":";for(auto itr=v.begin();itr!=v.end();itr++) cerr<<" "<<*itr; cerr<<endl
template<class T> bool chmax(T &a, const T &b) {if (a<b) { a = b; return true; } return false;}
template<class T> bool chmin(T &a, const T &b) {if (a>b) { a = b; return true; } return false;}
template<class T> void print(const T &t) { cout << t << "\n"; }
const ll INF = 1LL << 62;
const int iINF = 1 << 30;

int max_num = 101010;
using vi = vector<int>;
using Graph = vector<vi>;
Graph G(max_num);
vi cnt(max_num), color(max_num);
vector<bool> good(max_num);

void dfs(int v, int p = -1, int d = 0) {
    if(cnt[color[v]]==0) good[v]=true;
    cnt[color[v]]++;
    fore(nv, G[v]) {
        if (nv == p) continue;
        dfs(nv, v, d+1);
    }
    cnt[color[v]]--;
}

int n,a,b;

int main() {
    fio(); cin>>n;
    rep(i,n) cin>>color[i];
    rep(i,n-1) {
        cin>>a>>b;a--;b--;
        G[a].emplace_back(b);
        G[b].emplace_back(a);
    }
    dfs(0);
    rep(i,n) if(good[i]) print(i+1);
}


#include <iostream>
#include <iomanip>
#include <sstream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>
#include <utility>
#include <type_traits>
#include <cmath>
#include <cassert>
#include <cstdio>

using namespace std;
using namespace placeholders;

using LL = long long;
using ULL = unsigned long long;
using VI = vector< int >;
using VVI = vector< vector< int > >;
using VS = vector< string >;
using ISS = istringstream;
using OSS = ostringstream;
using PII = pair< int, int >;
using VPII = vector< pair< int, int > >;
template < typename T = int > using VT = vector< T >;
template < typename T = int > using VVT = vector< vector< T > >;
template < typename T = int > using LIM = numeric_limits< T >;
template < typename T = int > using OSI = ostream_iterator< T >;

template < typename T > inline istream& operator>>( istream &s, vector< T > &v ){ for ( T &t : v ) { s >> t; } return s; }
template < typename T > inline ostream& operator<<( ostream &s, const vector< T > &v ){ for ( int i = 0; i < int( v.size() ); ++i ){ s << ( " " + !i ) << v[i]; } return s; }

void in_impl(){};
template < typename T, typename... TS > void in_impl( T &head, TS &... tail ){ cin >> head; in_impl( tail ... ); }
#define IN( T, ... ) T __VA_ARGS__; in_impl( __VA_ARGS__ );

template < typename T > inline T fromString( const string &s ) { T res; istringstream iss( s ); iss >> res; return res; }
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); }

#define NUMBERED( name, number ) NUMBERED2( name, number )
#define NUMBERED2( name, number ) name ## _ ## number
#define REP1( n ) REP2( NUMBERED( REP_COUNTER, __LINE__ ), n )
#define REP2( i, n ) REP3( i, 0, n )
#define REP3( i, m, n ) for ( int i = ( int )( m ); i < ( int )( n ); ++i )
#define GET_REP( a, b, c, F, ... ) F
#define REP( ... ) GET_REP( __VA_ARGS__, REP3, REP2, REP1 )( __VA_ARGS__ )
#define FOR( e, c ) for ( auto &&e : c )
#define ALL( c ) begin( c ), end( c )
#define AALL( a ) ( remove_all_extents< decltype( a ) >::type * )a, ( remove_all_extents< decltype( a ) >::type * )a + sizeof( a ) / sizeof( remove_all_extents< decltype( a ) >::type )

#define SZ( v ) ( (int)( v ).size() )
#define EXISTS( c, e ) ( ( c ).find( e ) != ( c ).end() )

template < typename T > inline bool chmin( T &a, const T &b ){ if ( b < a ) { a = b; return true; } return false; }
template < typename T > inline bool chmax( T &a, const T &b ){ if ( a < b ) { a = b; return true; } return false; }

#define PB push_back
#define EM emplace
#define EB emplace_back
#define BI back_inserter

#define MP make_pair
#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

//     Λ   Λ＿_
//  ／(*ﾟーﾟ)／＼
// ／| ￣U U￣|＼／
//   |      |／

int main()
{
	cin.tie( nullptr );
	ios::sync_with_stdio( false );
	cout << setprecision( 12 ) << fixed;

	IN( int, N, M );

	if ( N == 1 && M == 0 )
	{
		cout << "1 2" << endl;
		return 0;
	}

	if ( M < 0 || N - 1 <= M )
	{
		cout << -1 << endl;
		return 0;
	}

	VPII res;
	res.EB( 1, 1 );
	--N;
	++M;
	for ( ; M; --M, --N )
	{
		const int l = res.back().snd + 1;
		res.EB( l, l + 1 );
	}
	res[0].snd = res.back().snd + 1;

	while ( N-- )
	{
		const int l = res.back().snd + 2;
		res.EB( l, l + 1 );
	}

	FOR( p, res )
	{
		cout << p.fst << ' ' << p.snd << '\n';
	}
	cout << flush;

	return 0;
}