Problem:
Score : 300 points

Problem Statement

1000000000000001 dogs suddenly appeared under the roof of Roger's house, all of which he decided to keep. The dogs had been numbered 1 through 1000000000000001, but he gave them new names, as follows:

the dogs numbered 1,2,\cdots,26 were respectively given the names a, b, ..., z;

the dogs numbered 27,28,29,\cdots,701,702 were respectively given the names aa, ab, ac, ..., zy, zz;

the dogs numbered 703,704,705,\cdots,18277,18278 were respectively given the names aaa, aab, aac, ..., zzy, zzz;

the dogs numbered 18279,18280,18281,\cdots,475253,475254 were respectively given the names aaaa, aaab, aaac, ..., zzzy, zzzz;

the dogs numbered 475255,475256,\cdots were respectively given the names aaaaa, aaaab, ...;

and so on.

To sum it up, the dogs numbered 1, 2, \cdots were respectively given the following names:

a, b, ..., z, aa, ab, ..., az, ba, bb, ..., bz, ..., za, zb, ..., zz, aaa, aab, ..., aaz, aba, abb, ..., abz, ..., zzz, aaaa, ...

Now, Roger asks you:

"What is the name for the dog numbered N?"

Constraints

N is an integer.

1 \leq N \leq 1000000000000001

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer to Roger's question as a string consisting of lowercase English letters.

Sample Input 1

2

Sample Output 1

b

Sample Input 2

27

Sample Output 2

aa

Sample Input 3

123456789

Sample Output 3

jjddja

Solution in C++ (Clang 10.0.0) (judge verdict: Accepted)

#include <iostream>
#include <functional>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <set>
#include <queue>
#include <map>
#include <iomanip>
#include <complex>
#include <random>
#include <bitset>
// #include <prettyprint.hpp>
using namespace std;
#define repi(i,n) for(int i=0;i<n;++i)
#define rep(i,n) for(ll i=0;i<n;++i)
#define repinvi(i,n) for(int i=n-1;i>=0;--i)
#define sll(n) scanf("%lld", &n);
#define sii(n) scanf("%d", &n);
#define slf(n) scanf("%lf", &n);
#define pll pair<ll,ll>
#define pii pair<int,int>
#define psi pair<si,si>
typedef long long ll;
typedef double lf;
typedef short int si;

ll lpower(ll b, ll p){
    if(b  < 2){
        return b;
    }

    if(p == 0){
        return 1;
    }

    if(p == 1){
        return b;
    }

    ll x = lpower(b, p/2);
    x *= x;
    if(p % 2){
        x *= b;
    }

    return x;
}

inline ll rsum(ll r, ll n){
    return r * (lpower(r, n) - 1) / (r - 1);
}

string alphabet = "abcdefghijklmnopqrstuvwxyz";


void Main(){
    ll N;
    cin >> N;

    ll length, left;
    rep(i, 12){
        ll r_sum = rsum(26, i);
        if(r_sum >= N){
            length = i;
            left = N - rsum(26, i-1);
            break;
        }
    }

    // cout << "length=" <<length <<endl;

    vector<ll> diff;
    for(ll j=length-1;j>=0;j--){
        ll base = lpower(26, j);
        if(base < left){
            ll num = (left-1) / base;
            left = left - base * num;
            diff.emplace_back(num);
        }else{
            ll num = 0;
            diff.emplace_back(num);
        }
    }

    string ans = "";
    for(ll i=diff.size()-1;i>=0;i--){
        ans = alphabet[diff[i]] + ans;
    }

    // cout << diff <<endl;

    
    cout << ans <<endl;


}

int main(){
    Main();
}