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#include <iostream>
#include <cstdio>

using namespace std;
#define LONG long long

LONG maxPos = 1LL;
LONG onePos = 0LL;
LONG theRest = 0LL;
LONG theMask = 1LL;
int  last = 0;

bool testPos(long chars, LONG pos)
{
    for(long idx = 1L; idx <= chars && idx < 63L; ++idx)
    {
        onePos += theMask;
        theMask <<= 1;
    }

    maxPos = onePos * 3LL;

    if(pos > maxPos)
        return false;

    return true;
}

char first(LONG position)
{
    if(position > (2LL * onePos))
    {
        last = 3;
        theRest = position - (2LL * onePos);
        return 'c';
    }
    else if(position > onePos)
    {
        last = 2;
        theRest = position - onePos;
        return 'b';
    }

    theRest = position;
    last = 1;
    return 'a';
}

char next()
{
   char ret = 'x';

   if(theMask & theRest)
   {
      switch(last)
      {
      case 3: 
         last = 2;
         ret = 'b';
         break;
      default:
         last = 3;
         ret = 'c';
      }
   }
   else
   {
      switch(last)
      {
      case 1: 
         last = 2;
         ret = 'b';
         break;
      default:
         last = 1;
         ret = 'a';
      }
   }

    return ret;
}

int main(int argc, char* argv[])
{
   long  charCount = 0L;
   LONG  position = 0LL;

   scanf("%ld %lld", &charCount, &position);
   
   if(!testPos(charCount, position))
   {
      printf("NIE\n");
   }
   else
   {

      printf("%c", first(position));

      if(theRest > 0LL)
      {
         while(!(theMask & theRest))
            theMask >>= 1;
         theMask >>= 1;
         while(theMask)
         {
            printf("%c", next());
            theMask >>= 1;
         }
      }
      
      printf("\n");  
   }
   return 0;
}