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
}

C++: #include<iostream>

char *chr, *peo;
int n,m;

void sitA(int i){
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'A';
			return;
		}
	}
}

void sitB(int i){
	if(chr[n-1] == '#' && chr[n-2] != 'A'){
		chr[n-1] = 'B';
		return;
	}
	for(int k=n-2; k>0; k--){
		if(chr[k] == '#' && chr[k-1] != 'A' && chr[k+1] != 'A'){
			chr[k] = 'B';
			return;
		}
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'B';
			return;
		}
	}
}

void sitC(int i){
	if(i==0){
		if(n%2 == 0)
			chr[n/2] = 'C';
		else
			chr[(n-1)/2] = 'C';
		return;
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#')
			continue;
		if(k<n-1){
			if(chr[k+1] == '#'){
				chr[k+1] = 'C';
				return;
			}
		}
		if(k>0){
			if(chr[k-1] == '#'){
				chr[k-1] = 'C';
				return;
			}
		}
	}
}

void sitD(int i){
	if(i==0){
		chr[0] = 'D';
		return;
	}
	int ans,tmp=0,tmp1,tmp2;
	for(int k=0; k<n; k++){
		if(chr[k] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		for(int t=k; t<n; t++){
			if(chr[t] != '#')
				break;
			tmp1++;
			if(t == n-1)
				tmp1 = n+1;
		}
		if(k == n-1)
			tmp1 = n+1;
		for(int t=k; t>=0; t--){
			if(chr[t] != '#')
				break;
			tmp2++;
			if(t == 0)
				tmp2 = n+1;
		}
		if(k == 0)
			tmp2 = n+1;
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
	}
	chr[ans] = 'D';
}

void solve(){
	char tmp;
	for(int i=0; i<m; i++){
		tmp = peo[i];
		switch(tmp){
		case 'a':
		case 'A':
			sitA(i);
			break;
		case 'b':
		case 'B':
			sitB(i);
			break;
		case 'c':
		case 'C':
			sitC(i);
			break;
		case 'd':
		case 'D':
			sitD(i);
			break;
		}
	}
	std::cout << chr << std::endl;
}

int main(){
	while(true){
		std::cin >> n >> m;
		if(!n && !m)
			return 0;
		chr = new char[n+1];
		peo = new char[m];
		for(int i=0; i<n; i++){
			chr[i] = '#';
			if(i<m)
				std::cin >> peo[i];
		}
		chr[n] = '\0';
		solve();
		delete[] chr;
		delete[] peo;
	}
}

C++: #include<iostream>
#include<string>
using namespace std;

int main()
{
	int n,m,i,j,s[102],temp,flag,max,z,count,left,right;
	char k;
	cin>>n>>m;

	while(n!=0){

	for(i=0;i<102;i++)
		s[i]=100;
	for(i=1;i<n+1;i++)
		s[i]=0;

	for(i=0;i<m;i++){
		max=0;
		cin>>k;
		if(k=='A'){
			for(j=1;j<n+1;j++){
				if(s[j]==0){
					s[j]=1;
				break;
				}
			}
		}else if(k=='B'){
			flag=0;
			for(j=n;j>0;j--){
				if(s[j]==0){
					if(s[j+1]!=1 && s[j-1]!=1){
						s[j]=2;
						flag=1;
						break;
					}
					else temp=j;
				}
			}
			if(flag==0){
				s[j]=temp;
				temp=0;
			}
		}else if(k=='C'){
			flag = 0;
			for(j=2;j<n;j++){
				if(s[j]==0 && s[j-1]!=0){
					s[j]=3;
					flag = 1;
					break;
				}
			}
			if(flag ==0){
				if(n%2==0){
					s[n/2+1]=3;
				}
				else {
					s[(n+1)/2]=3;
				}
			}
		}
		else if(k=='D'){
			temp=0;max=0;flag=0;
			for(j=n;j>0;j--){
				if(s[j]==0){
					left=0;right=0;
					for(z=1;;z++){
						if(s[j+z]!=0)
							break;
						else
							right++;
					}

					for(z=1;;z++){
						if(s[j-z]!=0)
							break;
						else 
							left++;
					}
						if(left>right)
							 temp=left;
						else temp=right;
	
				if(temp>=max){
					max=temp;
					flag=j;
				}
				}
			}
			s[flag]=4;
		}
	}


	for(i=1;i<n+1;i++){
		if(s[i]==0)
			cout<<'#';
		else if(s[i]==1)
			cout<<'A';
		else if(s[i]==2)
			cout<<'B';
		else if(s[i]==3)
			cout<<'C';
		else if(s[i]==4)
			cout<<'D';
	}

	cout<<"\n";

	cin>>n>>m;
	}

		return 0;
	}

C++: #include <bits/stdc++.h>
using namespace std;
int n,m;
char t[120];

void A(char a){
  int i=1;
  while(t[i]!=0) i++;
  t[i]=a;
}

void B(){
  for(int i=n;i>=1;i--){
    if(t[i]==0){
      t[i]='B';
      break;
    }
  }
}

void C(int cnt){
  if(cnt==0) {
    if(n%2) t[n/2+1]='C';
    else t[(n+1)/2]='C';
    return;
  }

  for(int i=1;i<=n;i++){
    if(t[i]!=0&&t[i+1]==0) {
      t[i+1]='C';
      break;
    }
    if(t[i]!=0&&t[i-1]==0){
      t[i-1]='C';
      break;
    }
  }
}

void D(int cnt){
  if(cnt==0){
    t[1]='D';
    return;
  }
  int mx=0,idx=0,c=0;
  for(int i=1;i<=n;i++) {
    if(t[i]==0) c++;
    else c=0;
    if(mx<c)mx=c,idx=i;
  }
  if(mx<=2){
    A('D');
    return ;
  }

  if(idx==n) t[n]='D';
  else   t[(idx-(idx-mx+1))/2+(idx-mx+1)]='D';
}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(t,0,sizeof(t));
    t[0]=t[n+1]=0;
    for(int i=0;i<m;i++){
      char a;
      cin >> a;
      if(a=='A')A(a);
      if(a=='B')B();
      if(a=='C')C(i);
      if(a=='D')D(i);
    }

    for(int i=1;i<=n;i++)if(t[i]==0)t[i]='#';
    for(int i=1;i<n;i++) cout <<t[i];
    cout <<t[n]<<endl;
  }
  return 0;
}