You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: b.go
    path of file: ./repos/codeforces-go/misc/gcj/2020/1c/b
    
    the code of the file until where you have to start completion: package main

import (
	"bufio"
	. "fmt"
	"io"
	"os"
	"sort"
)

type pair struct{ cnt, i int }
type pairs []pair

    
func run(_r io.Reader, _w io.Writer) {
	in := bufio.NewReader(_r)
	out := bufio.NewWriter(_w)
	defer out.Flush()

	solve := func(_case int) [10]byte {
		var ignore, s []byte
		Fscan(in, &ignore)
		heads := make(pairs, 26)
		for i := range heads {
			heads[i].i = i
		}
		vis := [26]bool{}
		for i := 0; i < 1e4; i++ {
			Fscan(in, &ignore, &s)
			heads[s[0]-'A'].cnt++
			for _, b := range s {
				vis[b-'A'] = true
			}
		}
		sort.Sort(heads)
		ans := [10]byte{}
		for i, p := range heads[:9] {
			ans[i+1] = byte('A' + p.i)
			vis[p.i] = false
		}
		for i, v := range vis {
			if v {
				ans[0] = byte('A' + i)
				break
			}
		}
		return ans
	}

	var t int
	Fscan(in, &t)
	for _case := 1; _case <= t; _case++ {
		Fprintf(out, "Case #%d: %s\n", _case, solve(_case))
	}
}