1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
#include <iostream>
#include <cmath>
using namespace std;

char getLetterByIndex(int index)
{
    return (char)(index + ((int)'a'));
}

int getIndexByLetter(char letter)
{
    return ((int)letter) - ((int)'a');
}

unsigned long long int integer_pow(long long int x, long long int n)
{
    unsigned long long int r = 1;
    while (n--)
        r *= x;

    return r; 
}

unsigned long long int getMaxWordsCount(long long int n)
{
    return 3 * (integer_pow(2,n) - 1); // zredukowany wzor na sume ciagu geometrycznego gdzie q=2,n=n,a1=3
}

unsigned long long int getMaxWordsCountWhenPrefixed(long long int n)
{
    return (integer_pow(2,n) - 1); // zredukowany wzor na sume ciagu geometrycznego gdzie q=2,n=n,a1=3
}

int slo2(long long int n, long long int k)
{
    long long int currentK, currentHalf;
    
    char previousLetter = 'x';
    char currentLetter;
    char letters[3][2];
    letters[0][0] = 'b';
    letters[0][1] = 'c';
    letters[1][0] = 'a';
    letters[1][1] = 'c';
    letters[2][0] = 'a';
    letters[2][1] = 'b';
    
    /*cout << "getMaxWordsCount(n = 63) " << getMaxWordsCount(63) << "\n";
    cout << "getMaxWordsCount(n = 62) " << getMaxWordsCount(62) << "\n";
    cout << "getMaxWordsCount(n = 61) " << getMaxWordsCount(61) << "\n";
    cout << "getMaxWordsCount(n = 60) " << getMaxWordsCount(60) << "\n";
    cout << "getMaxWordsCount(n = 59) " << getMaxWordsCount(59) << "\n";
    cout << "getMaxWordsCount(n = 58) " << getMaxWordsCount(58) << "\n";
    cout << "getMaxWordsCount(n = 57) " << getMaxWordsCount(57) << "\n";
    */
    
    /*
getMaxWordsCount(n = 63)  9223372036854775805 <- przepelnienie
getMaxWordsCount(n = 62) 13835058055282163709
getMaxWordsCount(n = 61)  6917529027641081853
getMaxWordsCount(n = 60)  3458764513820540925
getMaxWordsCount(n = 59)  1729382256910270461
getMaxWordsCount(n = 58)   864691128455135229
getMaxWordsCount(n = 57)   432345564227567613
---------------------------------------------
10^18                     1000000000000000000 (czyli maksymalne dane k)
*/
    
    
    long long int maxWordsCount, oneThirdOfMax, halfOfMax;
    long long int tmp = 0;
    
    long long int powerLimit = 59; // should be 59

    
    if (n < powerLimit) { // n powyzej 59 ma wiecej slow niz dla maksymalnego danego k (10^18) - patrz wyniki wyzej
        
        maxWordsCount = getMaxWordsCount(n);
        //cout << "maxWordsCount: " << maxWordsCount << "\n";
        
        if (k > maxWordsCount) { 
            cout << "NIE";
            return 0;
        }
        
        oneThirdOfMax = maxWordsCount / 3;
        
        //cout << "ceil((float)k / oneThirdOfMax) -1 -> " << ceil((float)k / oneThirdOfMax) -1 << "\n";
        //cout << "((int)ceil(k / oneThirdOfMax) - 1) -> " <<  ((int)ceil(k / oneThirdOfMax) - 1) << "\n";
        //cout << (char)((int)'a' + ceil(k / oneThirdOfMax) - 1) << "\n";
        
        previousLetter = getLetterByIndex((int)ceil((float)k / oneThirdOfMax) - 1);
        //cout << "\n";
        cout << previousLetter; // print first letter
        
        
        currentK = (k-1) % oneThirdOfMax;   
    } else {
    
    
        tmp = n;
        while (n >= powerLimit) {
            previousLetter = (previousLetter == 'a') ? 'b' : 'a';
            //cout << "\n";
            cout << previousLetter;
            n--;
            k--;
            
            //if (k == 0) {
            //    break;
            //}   
        }
        if (n < tmp) {        
            n++;
            k++;
        }
        
        currentK = k-1;
    }
    
    
    
    
    
    
    
    
    while (n > 1) {
        //cout << "currentK: " << currentK << "\n";
        if (currentK == 0) {
            return 0;
        }
        
        maxWordsCount = getMaxWordsCountWhenPrefixed(n);
        halfOfMax = (long long int)floor((maxWordsCount-1) / 2);
        
        currentHalf = (currentK <= halfOfMax) ? 0 : 1;
        
        /*cout << "previousLetter: " << previousLetter << "\n";
        cout << "maxWordsCount: " << maxWordsCount << "\n";
        cout << "halfOfMax: " << halfOfMax << "\n";
        cout << "currentHalf: " << currentHalf << "\n";
        cout << "getIndexByLetter(previousLetter): " << getIndexByLetter(previousLetter) << "\n";
        */
        
        currentLetter = letters[getIndexByLetter(previousLetter)][currentHalf];
        //cout << "\n";
        cout << currentLetter;
        previousLetter = currentLetter;
    
        //maxWordsCount = oneThirdOfMax;
        //oneThirdOfMax = (long long int)((maxWordsCount-1)/2);
        //currentK = (currentK-1) % oneThirdOfMax;
        
        currentK = (currentK-1) % halfOfMax;
        
        n--;
    }
    
    return 0;
}


int main() {
    long long int n;
    long long int k;
    cin >> n;
    cin >> k;
    
    long long int i = k;
    
    while (i<=k) {
        slo2(n, i);
        //cout << "  " << i << "\n";
        i++;
    }
    
    return 0;
}