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
#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long LL;

const int N = 1e6 + 7;
int n;
LL k, pot[N], x;
char s[N];

inline char mn(char z)
{
    return (z == 'a' ? 'b' : 'a');
}

inline char mx(char z)
{
    return (z == 'c' ? 'b' : 'c');
}

int main()
{
    scanf("%d%lld", &n, &k);
    pot[0] = 1;
    for(int i = 1; i <= n + 3; i++)
        pot[i] = min(2 * pot[i - 1], (LL)1e18 + 7);
    x = pot[n] - 1;
    if(k <= x)
        s[0] = 'a';
    else if(k <= 2 * x)
        s[0] = 'b', k -= x;
    else if(k <= 3 * x)
        s[0] = 'c', k -= 2 * x;
    else
    {
        puts("NIE");
        return 0;
    }
    for(int i = 1; i < n; i++)
    {
        if(k == 1) continue;
        if(k <= pot[n - i])
            s[i] = mn(s[i - 1]), k--;
        else
            s[i] = mx(s[i - 1]), k -= pot[n - i];
    }
    printf("%s\n", s);
    return 0;
}