#include <stdio.h>
#include <stack>
typedef long long ll;

int main(void) {
  ll n;
  std::stack<char> s;
  scanf("%lld", &n);
  while(n) s.push(--n % 26 + 'a'), n /= 26;
  while(s.size()) printf("%c", s.top()), s.pop();
  return 0;
}