package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func maxRunsFromCF(first, last, length int) int {
	if length == 1 {
		if first == 1 {
			return 1
		}
		if first == 2 {
			return 2
		}
		return 3
	}
	runs := length
	if first > 1 {
		runs++
	}
	if last > 1 {
		runs++
	}
	return runs
}

func getCF(r, q int) []int {
	res := make([]int, 0, 32)
	for q != 0 {
		res = append(res, r/q)
		r, q = q, r%q
	}
	return res
}

func buildRuns(cf []int) []int {
	t := len(cf)
	if t == 1 {
		x := cf[0]
		if x == 1 {
			return []int{1}
		}
		if x == 2 {
			return []int{1, 1}
		}
		return []int{1, x - 2, 1}
	}

	res := make([]int, 0, t+2)
	if cf[0] > 1 {
		res = append(res, 1, cf[0]-1)
	} else {
		res = append(res, 1)
	}
	for i := 1; i < t-1; i++ {
		res = append(res, cf[i])
	}
	if cf[t-1] > 1 {
		res = append(res, cf[t-1]-1, 1)
	} else {
		res = append(res, 1)
	}
	return res
}

func main() {
	in := bufio.NewReaderSize(os.Stdin, 1<<20)
	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	defer out.Flush()

	var n, r int
	if _, err := fmt.Fscan(in, &n, &r); err != nil {
		return
	}

	if n == 1 && r == 1 {
		out.WriteString("0\nT\n")
		return
	}

	if n > r || r < 1 || n < 1 {
		out.WriteString("IMPOSSIBLE\n")
		return
	}

	bestRuns := -1
	bestQ := -1

	for q := 1; q < r; q++ {
		a, b := r, q
		sum := 0
		length := 0
		first := 0
		last := 0
		ok := true

		for b != 0 {
			quo := a / b
			sum += quo
			if sum > n {
				ok = false
				break
			}
			length++
			if length == 1 {
				first = quo
			}
			last = quo
			a, b = b, a%b
		}

		if !ok || a != 1 || sum != n {
			continue
		}

		runs := maxRunsFromCF(first, last, length)
		if runs > bestRuns {
			bestRuns = runs
			bestQ = q
			if bestRuns == n {
				break
			}
		}
	}

	if bestQ == -1 {
		out.WriteString("IMPOSSIBLE\n")
		return
	}

	cf := getCF(r, bestQ)
	runs := buildRuns(cf)
	mistakes := n - len(runs)

	ops := make([]byte, n)
	pos := 0
	ch := byte('T')
	for _, cnt := range runs {
		for i := 0; i < cnt; i++ {
			ops[pos] = ch
			pos++
		}
		if ch == 'T' {
			ch = 'B'
		} else {
			ch = 'T'
		}
	}

	out.WriteString(strconv.Itoa(mistakes))
	out.WriteByte('\n')
	out.Write(ops)
	out.WriteByte('\n')
}