#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define pb push_back
#define ar array
#define all(x) x.begin(), x.end()
#define siz(x) (int)x.size()
#define FOR(x, y, z) for(int x = (y); x < (z); x++)
#define ROF(x, z, y) for(int x = (y-1); x >= (z); x--)
#define F0R(x, z) FOR(x, 0, z)
#define R0F(x, z) ROF(x, 0, z)
#define trav(x, y) for(auto&x:y)
using ll = long long;
using vi = vector<int>;
using vl = vector<long long>;
using pii = pair<int, int>;
using vpii = vector<pair<int, int>>;
template<class T> inline bool ckmin(T&a, T b) {return b < a ? a = b, 1 : 0;}
template<class T> inline bool ckmax(T&a, T b) {return b > a ? a = b, 1 : 0;}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const char nl = '\n';
const int mxN = 1e6 + 10;
const int MOD = 1e9 + 7;
const long long infLL = 1e18;
#ifdef ACMX
void answer(vi a, vi b, vi c){
trav(x, a){
cout << x << ' ';
}
cout << nl;
F0R(i, siz(b)){
cout << b[i] << ' ' << c[i] << endl;
}
}
#else
#include "doll.h"
#endif
int switches, m, n, p2 = 1, val = 1; vi x(mxN), y(mxN), c, a, arr;
vi label(int node){
if(node >= p2) return vi{node - p2};
vi l = label(node*2);
vi r = label(node*2 + 1);
vi res;
F0R(i, siz(l)){
res.pb(l[i]);
res.pb(r[i]);
}
return res;
}
int bruh = 0;
int dfs(int u, int l, int r){
if(r < p2 - n){
return -1;
}
if(l == r){
return a[arr[l]];
}
int xyz = u;
int m = (l + r)/2;
bruh++;
x[xyz] = dfs(bruh, l, m);
y[xyz] = dfs(bruh, m+1, r);
return -u-1;
}
void create_circuit(int M, vi A){
a = A, m = M; n = siz(a);
F0R(i, m+1){
c.pb(-1);
}
while(p2 <= n){
p2*=2;
}
n++;
arr = label(1);
set<int> com;
map<int, int> mp;
FOR(i, p2 - n, p2){
com.insert(arr[i]);
}
int ctr = 0;
trav(v, com){
mp[v] = ctr++;
}
FOR(i, p2-n, p2){
arr[i] = mp[arr[i]];
}
a.pb(0);
dfs(0, 0, p2-1);
x.resize(bruh);
y.resize(bruh);
//assert(x.size() <= (n-1)+log2(n-1));
answer(c, x, y);
}
#ifdef ACMX
int32_t main(){
ios_base::sync_with_stdio(0); cin.tie(0);
int m, n;
cin >> m >> n;
vi tmp;
F0R(i, n){
int foo; cin >> foo;
tmp.pb(foo);
}
create_circuit(m, tmp);
return 0;
}
#endif
