Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)
const INF = 0x7FFFFFFF

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		n, _ := strconv.Atoi(buf[0])
		m, _ := strconv.Atoi(buf[1])
		if n == 0 && m == 0 {
			break
		}
		chairs := make([]string, n)
		for i := range chairs {
			chairs[i] = "#"
		}
		sit := func(who string) {
			if who == "A" {
				chairs[getStringIndex(chairs, "#")] = "A" // A国の人は左から見て行って空いている席を見つけ次第座る
				// log.Println(chairs)
			} else if who == "B" {
				f := true
				for i := n-1; i > -1; i-- {
					// B国の人はA国人の隣以外で、右端から空いている椅子に座る
					if chairs[i] == "#" && (i == 0 || chairs[i-1] != "A") && (i == n-1 || chairs[i+1] != "A") {
								chairs[i] = "B"
								f = false
								break
					}
				}
				// A国人の隣しか空いていない場合、我慢して左端から空いている椅子に座る
				if f {
					chairs[getStringIndex(chairs, "#")] = "B"
				}
				// log.Println(chairs)
			} else if who == "C" { // C国人は人の隣に座りたい
				for i := 0; i < n; i++ {
					if chairs[i] != "#" {
						if i + 1 <= n-1 && chairs[i+1] == "#" {
							chairs[i+1] = "C"
							break
						} else if i - 1 >= 0 && chairs[i-1] == "#" {
							chairs[i-1] = "C"
							break
						}
					}
				}
				// log.Println(chairs)
			} else { // who == "D"
				// D国の人は人から離れて座りたい
				// どうしても誰かの隣に座らなければならない場合、その中で一番左側にある椅子に座る
				scores := make([]int, n)
				for i := range scores {
					scores[i] = INF
				}
				for i, v := range chairs {
					if v == "#" {
						scores[i]++
					}
				}
				for i := n-1; i > -1; i-- {
					tmp := 0
					if chairs[i] == "#" {
						tmp++
					} else {
						tmp = 0
					}
					scores[i] = min(scores[i], tmp)
				}
				chairs[getIntIndex(scores, getMax(scores))] = "D"
				// log.Println(chairs)
			}
		}
		scanner.Scan()
		if first := scanner.Text(); first == "A" || first == "D" {
			chairs[0] = first
		} else if first == "B" {
			chairs[len(chairs)-1] = "B"
		} else {
			chairs[n/2] = "C"
		}
		// log.Println(chairs)
		for i := 0; i < m-1; i++ {
			scanner.Scan()
			sit(scanner.Text())
		}
		fmt.Println(strings.Join(chairs, ""))
	}
}

func getStringIndex(chairs []string, who string) int {
	for i, v := range chairs {
		if v == who {
			return i
		}
	}
	return -1
}

func getIntIndex(scores []int, target int) int {
	for i, v := range scores {
		if v == target {
			return i
		}
	}
	return -1
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func getMax(scores []int) int {
	tmp := -1
	for _, v := range scores {
		if tmp < v {
			tmp = v
		}
	}
	return tmp
}

Python: INF = 10**10
while(True):
    N, M = [int(n) for n in input().split()]
    if N + M == 0:
        break
    chair = ["#" for _ in range(N)]
    for i in range(M):
        a = str(input())
        if a == "A":
            for i in range(N):
                if chair[i] == "#":
                    chair[i] = "A"
                    break
        elif a == "B":
            OK = False
            for i in range(N-1, -1, -1):
                if chair[i] == "#":
                    if i != 0 and chair[i-1] == "A":
                        continue
                    if i != N-1 and chair[i+1] == "A":
                        continue
                    chair[i] = "B"
                    OK = True
                    break
            if OK:
                continue
            for i in range(N):
                if chair[i] == "#":
                    chair[i] = "B"
                    break
        elif a == "C":
            if chair.count("#") == N:
                chair[(N)//2] = "C"
                continue
            OK = False
            for i in range(N):
                if chair[i] != "#":
                    if i != N-1 and chair[i+1] == "#":
                        chair[i+1] = "C"
                        OK = True
                        break
                    if i != 0 and chair[i-1] == "#":
                        chair[i-1] = "C"
                        OK = True
                        break
        elif a == "D":
            if chair.count("#") == N:
                chair[0] = "D"
                continue
            start = False
            distmap = [0 for _ in range(N)]
            dist = 0
            for i in range(N):
                if chair[i] != "#":
                    dist = 0
                    distmap[i] = dist
                    start = True
                elif start:
                    dist += 1
                    distmap[i] = dist
                else:
                    distmap[i] = INF
            start = False
            for i in range(N-1, -1, -1):
                if chair[i] != "#":
                    dist = 0
                    distmap[i] = min(dist, distmap[i])
                    start = True
                elif start:
                    dist += 1
                    distmap[i] = min(dist, distmap[i])
            target = max(distmap)
            for i in range(N):
                if distmap[i] == target and chair[i] == "#":
                    chair[i] = "D"
                    break
    print("".join(chair))

Python: INF = 10 ** 20

while True:
  n, m = map(int, input().split())
  if not n:
    break

  chairs = list("#" * n)

  def sit(s):
    if s == "A":
      chairs[chairs.index("#")] = "A"
    
    elif s == "B":
      for i in range(n - 1, -1, -1):
        if chairs[i] == "#" and (i == 0 or chairs[i - 1] != "A") and (i == n - 1 or chairs[i + 1] != "A"):
          chairs[i] = "B"
          break
      else:
        chairs[chairs.index("#")] = "B"

    elif s == "C":
      for i in range(0, n):
        if chairs[i] != "#":
          if i - 1  >= 0 and chairs[i - 1] == "#":
            chairs[i - 1] = "C"
            break
          elif i + 1 <= n - 1 and chairs[i + 1] == "#":
            chairs[i + 1] = "C"
            break

    else:
      score = [INF for _ in range(n)]
      dist = INF
      for i in range(n):
        if chairs[i] == "#":
          dist += 1
        else:
          dist = 0
        score[i] = dist

      dist = INF
      for i in range(n - 1, -1, -1):
        if chairs[i] == "#":
          dist += 1
        else:
          dist = 0
        score[i] = min(score[i], dist)
      high_score = max(score)
      chairs[score.index(high_score)] = "D"
  
  first = input()
  if first in ["A", "D"]:
    chairs[0] = first
  elif first == "B":
    chairs[-1] = "B"
  else:
    chairs[n // 2] = "C"
  for _ in range(m - 1):
    sit(input())

  print("".join(chairs))

Python: INF = 10 ** 20

while True:
  n, m = map(int, input().split())
  if not n:
    break

  chairs = list("#" * n)

  def sit(s):
    if s == "A":
      chairs[chairs.index("#")] = "A"
    
    elif s == "B":
      for i in range(n - 1, -1, -1):
        if chairs[i] == "#" and (i == 0 or chairs[i - 1] != "A") and (i == n - 1 or chairs[i + 1] != "A"):
          chairs[i] = "B"
          break
      else:
        chairs[chairs.index("#")] = "B"

    elif s == "C":
      for i in range(n):
        if chairs[i] != "#":
          if i + 1 <= n - 1 and chairs[i + 1] == "#":
            chairs[i + 1] = "C"
            break
 
          elif i - 1  >= 0 and chairs[i - 1] == "#":
            chairs[i - 1] = "C"
            break

    else:
      score = [INF for _ in range(n)]
      dist = INF
      for i in range(n):
        if chairs[i] == "#":
          dist += 1
        else:
          dist = 0
        score[i] = dist

      dist = INF
      for i in range(n - 1, -1, -1):
        if chairs[i] == "#":
          dist += 1
        else:
          dist = 0
        score[i] = min(score[i], dist)
      high_score = max(score)

      chairs[score.index(high_score)] = "D"
  
  first = input()
  if first in ["A", "D"]:
    chairs[0] = first
  elif first == "B":
    chairs[-1] = "B"
  else:
    chairs[n // 2] = "C"
  
  for _ in range(m - 1):
    sit(input())
  print("".join(chairs))