func_code_string: #include <bits/stdc++.h>   using namespace std;   template <class T1, class T2>   inline istream& operator>>(istream& fin, pair<T1, T2>& pr) {     fin >> pr.first >> pr.second;     return fin;   }   template <class T0, class T1, class T2>   inline istream& operator>>(istream& fin, tuple<T0, T1, T2>& t) {     fin >> get<0>(t) >> get<1>(t) >> get<2>(t);     return fin;   }   template <class T>   inline istream& operator>>(istream& fin, vector<T>& a) {     if (!a.size()) {       size_t n;       fin >> n;       a.resize(n);     }     for (auto& u : a) fin >> u;     return fin;   }   string probB() {     vector<string> a(2);     cin >> a;     const auto n = a[0].length();     size_t diff = 0;     for (size_t i = 0; i < n; ++i) diff += a[0][i] != a[1][i];     if (diff & 1) return  impossible ;     string str;     size_t k = 0;     for (size_t i = 0; i < n; ++i)       if (a[0][i] == a[1][i])         str.push_back(a[0][i]);       else if (2 * k < diff)         str.push_back(a[0][i]), ++k;       else         str.push_back(a[1][i]);     return str;   }   int main(const int argc, char* argv[]) {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     ;     cout << probB();     return EXIT_SUCCESS;   }   