// yukicoder 327 (http://yukicoder.me/problems/904)
#include<cstdio>
#include<vector>
#define repd(i,a) for(int i=(a);i>=0;--i)

typedef long long ll;

ll N;

std::vector<int> vs;

int main()
{
	scanf( "%lld", &N );

	if( N <= 25 )
	{ putchar( 'A'+N ); puts(""); return 0; }	

	N -= 26;

	while( N > 0 )
		vs.push_back( N%26 ), N /= 26;

	while( vs.size() < 2 )
		vs.push_back( 0 );

	repd( i, vs.size()-1 )
		putchar( 'A'+vs[i]-(i>=2?vs.size()>=3:0) );

	puts("");

	return 0;
}