#include <bits/stdc++.h>

long table1[20];
long table2[20];

void init() {
  long temp = 1;
  for(int i = 0; i < 10; ++i) {
    table1[i] = temp;
    temp *= 26;
  }
  long sum = -1;
  for(int i = 0; i < 10; ++i) {
    sum += table1[i];
    table2[i] = sum;
  }
}

std::string solve(long N) {
  std::string temp;
  for(int i = 0; i < 10; ++i) {
    if( table2[i] <= N ) {
      temp += (N - table2[i]) / table1[i] % 26 + 'A';
    }
  }
  std::reverse(temp.begin(), temp.end());
  return temp;
}

int main() {
  init();
  
  long N;
  std::cin >> N;
  std::cout << solve(N) << std::endl;
  
  return 0;
}