#include <cstdio>
#include <string>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int ss;
int f(const string& strs) {string s("##");for(string::const_iterator it = strs.begin(); it != strs.end(); ++it) {s.push_back(*it);s.push_back('#');}int len = s.length(), id = 0, mx = 0;vector<int> p(len, 0);for(int i = 1; i < len; ++i) {p[i] = mx > i ? min(mx - i, p[2*id-i]) : 1;while(s[i+p[i]] == s[i-p[i]]) {++p[i];}if(i + p[i] > mx) {mx = i + p[i];id = i;}}int start = 0, sublen = 0;for(int i = 1; i < len; ++i) {if(p[i] > sublen) {sublen = p[i];start = i;}}return sublen - 1;
}
int main(){//pre();int n,m;int T;cin>>T;for(int t = 1 ; t <= T ; t++){scanf("%d%d",&m,&n);printf("Case #%d: ",t);if(m == 1){for(int i = 0 ; i < n ; i++) printf("a");}else if(m >= 3){for(int i = 0 ; i < n ; i++) {if(i%3 == 0) putchar('a');if(i%3 == 1) putchar('b');if(i%3 == 2) putchar('c');}}else if(m == 2){if(n == 1) printf("a");if(n == 2) printf("ab");if(n == 3) printf("aab");if(n == 4) printf("aabb");if(n == 5) printf("aaaba");if(n == 6) printf("aaabab");if(n == 7) printf("aaababb");if(n == 8) printf("aaababbb");if(n >= 9){string a = "aaaa";for(int i = 4; i < n ;){if(i+4<n) {a+="babb";i+=4;}if(i+4>=n) {if(i+1==n) a+="a";if(i+2==n) a+="aa";if(i+3==n) a+="aaa";if(i+4==n) a+="aaaa";break;}if(i+4<n) {a+="aaba";i+=4;}if(i+4>=n) {if(i+1==n) a+="b";if(i+2==n) a+="bb";if(i+3==n) a+="bba";if(i+4==n) a+="bbaa";break;}if(i+4<n) {a+="bbaa";i+=4;}if(i+4>=n) {if(i+1==n) a+="a";if(i+2==n) a+="aa";if(i+3==n) a+="bab";if(i+4==n) a+="babb";break;}}cout<<a;}}putchar('\n');}return 0;
}