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


#define REP(i, n) for(int i = 0; i < (int)(n); i++)
#define FOR(i,n,m) for (int i=n; i<(int)(m); i++)
#define INF 1000000007
#define mp make_pair

typedef long long ll;
typedef long double ld;
ll dy[4]={-1,1,0,0};
ll dx[4]={0,0,1,-1};

/*---------- template ----------*/
ll N;
int main(){

	cin >> N;

	ll t=1;
	ll s=0;
	int leng=0;
	FOR(i,1,10){
		t*=26;
		s+=t;
		if(s >= N){
			s-=t;
			N-=s;
			leng=i;
			break;
		}
	}

	string ans="";
	while(N!=0){
		int t=N%26;
		ans=char('A'+t)+ans;
		N/=26;
	}

	REP(i,leng-ans.size()){
		ans=ans+'A';
	}

	cout << ans << endl;

	return 0;
}