#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <vector>

#include <queue>

#include <cstring>

#include <string>

#include <algorithm>

using namespace std;

typedef  long long  ll;

typedef unsigned long long ull;

#define MM(a,b) memset(a,b,sizeof(a));

#define inf 0x7f7f7f7f

#define FOR(i,n) for(int i=1;i<=n;i++)

#define CT continue;

#define PF printf

#define SC scanf

const int mod=1000000007;

const int N=1e6+10;

char s[2005][2005];

int flag[2005];

int main()

{

    int n;

    while(~scanf("%d",&n))

    {

        MM(s,'\0');

        if(n==1) {printf("1 : a\n");continue;}

        if(n==2) {

                printf("1 : NO\n");

                printf("2 : ab\n");

                continue;

       }

       for(int i=1;i<=3;i++) s[n][i]='a'+i-1;

       for(int i=4;i<=n;i++) s[n][i]='z';

       int p=3;

       for(int i=n-1;i>=1;i--)

       {

           int j;

           for(j=1;j<=p;j++)

               s[i][j]=s[i+1][j];

           if(s[i][p]=='a') s[i][j]='b';

           if(s[i][p]=='b') s[i][j]='c';

           if(s[i][p]=='c') s[i][j]='a';

           for(j++;j<=n;j++) s[i][j]='z';

           p++;

       }

       for(int i=1;i<=2;i++) printf("%d : NO\n",i);

       for(int i=3;i<=n;i++) printf("%d : %s\n",i,s[i]+1);

    }

    return 0;

}