#include <iostream>
#include <map>
#include <sstream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
string textinput;
getline(cin, textinput);
stringstream ss(textinput);
string word;
map<string, int> wordCount;
// Count the occurrences of each word
while(ss >> word) {
wordCount[word]++;
}
vector<string> repeatedWords;
// Check which words have been repeated
for(auto &it: wordCount) {
if(it.second > 1) {
repeatedWords.push_back(it.first);
}
}
// Sort words lexicographically
sort(repeatedWords.begin(), repeatedWords.end());
if(repeatedWords.empty()) {
cout << "NA" << endl;
} else {
for(size_t i = 0; i < repeatedWords.size(); ++i) {
cout << repeatedWords[i];
if(i < repeatedWords.size() - 1) cout << " ";
}
cout << endl;
}
return 0;
}