#include <bits/stdc++.h>
#define subs(a, b) substr(a, b-a+1)
#define hash _hash
#define int int64_t
using namespace std;
int p1 = 1e9 + 7, p2 = 1e9 + 9;
int hash(string str){
long long num = 1;
long long ans=0;
for(int i=0;i<(int)str.size();i++){
ans += (num * (int64_t)(str[i] - 'A' + 1))%p2;
// cout << "POS " << i << ": " << (num * (int64_t)(str[i] - 'A' + 1)) << "\n";
ans %= p2;
num = (num * p1)%p2;
}
// cout << "VAL: " << num << "\n";
return ans;
}
int pot(long long a, long long b, long long m){
long long r = 1;
while(b){
if(b&1) r = (r * (a%m))%m;
a = ((a%m) * (a%m))%m;
b /= 2;
}
return r;
}
int pref[2000001], suff[2000001];
int32_t main() {
int n;
cin >> n;
string str;
cin >> str;
pref[0] = (str[0] - 'A' + 1);
long long aux = p1;
for(int i=1;i<n;i++){
pref[i] = (pref[i-1] + aux * (str[i] - 'A' + 1))%p2;
aux = (aux*p1)%p2;
}
suff[n-1] = (str[n-1] - 'A' + 1);
for(int i=n-2;i>=0;i--){
suff[i] = ((str[i] - 'A' + 1) + (p1 * (long long)suff[i+1])%p2)%p2;
}
cout << "HASH: " << hash(str) << "\n";
// cout << (pref[2] + ((pot(p1, 3, p2) * (int64_t)suff[4]))%p2)%p2 << "\n";
if(n%2 == 0){
cout << "NOT POSSIBLE\n";
return 0;
}
int resp = -1, val = 0;
int k = (n-1)/2;
for(int i=0;i<n;i++){
int h1 = 0, h2 = 0;
if(i < k){
if(i == 0) h1 = ((pref[k] - pref[0])*pot(p1, p2-2, p2) + p2)%p2;
else h1 = ( pref[i-1] + ((pref[k] - pref[i])*pot(p1, (p2-2), p2))%p2 + p2) % p2;
h2 = suff[k+1];
}else{
h1 = pref[k-1];
h2 = ((pref[i-1] - pref[k-1]) + (suff[i+1] * pot(p1, (i-k), p2)%p2 + p2))%p2;
}
// cout << h1 << " " << h2 << "\n";
if(h1 == h2){
if(resp != -1 && resp != h1){
cout << "NOT UNIQUE\n";
return 0;
}
resp = h1;
val = i;
}
}
if(resp == -1){
cout << "NOT POSSIBLE\n";
}else{
for(int i=0;i<n;i++)
if(i != val) cout << str[i] << " ";
cout << "\n";
}
}
