#include<iostream>
#include<algorithm>

using namespace std;

int main(){

	long long N;
	long long kisu=26;
	int i=26;

	cin>>N;

	while(N>=kisu) kisu*=++i;
	kisu/=i--;

	while(kisu!=1){
		cout<<(char)(N/(kisu)-1+'A');
		N-=kisu*(N/kisu);
		kisu/=i--;
	}
	cout<<(char)(N+'A')<<endl;
}