https://pintia.cn/problem-sets/994805260223102976/problems/1071785884776722432
#include <iostream>
#include <string>
using namespace std;
int main(){
string A, B;
int h[300] = {0};
getline(cin, A); getline(cin, B);
A += B;
for(int i = 0; i < A.size(); i++){
if(!h[A[i]]){
cout << A[i];
h[A[i]]++;
}
}
return 0;
}