#include <iostream>
#include <algorithm>
#include <string>
#include <set>

using namespace std;

class Learner {
 private:
  set<string> dict;

 public:
  int Learn(const vector<string>& words) {
    int currNum=dict.size();
    return dict(begin(words),end(words)).size() - currNum;
  }
  vector<string> KnownWords() {
       return {dict.begin(), dict.end()};
  }
};