Language: C++

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433L;

template <class T> vector<T> multivector(size_t N,T init){return vector<T>(N,init);}
template <class... T> auto multivector(size_t N,T... t){return vector<decltype(multivector(t...))>(N,multivector(t...));}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max(a,b);}
template <class T> void chmin(T& a, const T b){a=min(a,b);}
void YN(bool flg) {cout << (flg ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << (flg ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << (flg ? "yes" : "no") << endl;}

/*
 * @title NBase
 */
class NBase{
public:
	inline static vector<long long> translate(long long X,long long N) {
		assert(abs(N)>1);
		vector<long long> res;
		while(1) {
			long long b = (X%abs(N)+abs(N)) % abs(N);
			res.push_back(b);
			(X -= b) /= N;
			if(X==0) break;
		}
		return res;
	}
	//Digit Sum
	inline static constexpr long long digit_sum(long long N, long long K) {
		long long sum = 0;
		for (; N > 0; N /= K) sum += N % K;
		return sum;
	}
};


int main() {
    ll N; cin >> N; N--;
    vector<ll> A(13);
    A[0]=26;
    for(int i = 1; i < 13; ++i) A[i] = 26*A[i-1];
    int idx = -1;
    for(int i = 0; i < 13; ++i) if(A[i]<=N) {
        N -= A[i];
        idx = i;
    }
    corner(idx==-1,char('a'+N));
    auto t = NBase::translate(N,26);
    string S = string(idx+2,'a');
    // print(N,idx);
    // print(t);
    // print(S);
    for(int i = 0; i < t.size(); ++i) {
        S[i] = char(t[i]+'a');
    }
    reverse(ALL(S));
    cout << S << endl;
    
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:80:10: error: ambiguous overload for 'operator<<' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   80 |     cout << S << endl;
      |     ~~~~ ^~ ~
      |     |       |
      |     |       std::string {aka std::__cxx11::basic_string<char>}
      |     std::ostream {aka std::basic_ostream<char>}
a.cc:25:60: note: candidate: 'std::ostream& operator<<(std::ostream&, const T<U>&) [with T = std::__cxx11::basic_string; U = char; std::ostream = std::basic_ostream<char>]'
   25 | template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
      |                                                            ^~~~~~~~
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/basic_string.h:4077:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]'
 4077 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~