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>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <complex>
#include <cstring>
#include <cstdlib>
#include <string>
#include <cmath>
#include <queue>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
const int INF = 1<<29;

int main() {
  int n, m;
  while(cin>>n>>m,n+m) {
    vector<char> v(n, '#');
    REP(j,m) {
      char c;
      cin >> c;
      if (c=='A') {
        REP(i,n) {
          if (v[i] == '#') {
            v[i] = c;
            break;
          }
        }
      } else if (c=='B') {
        bool f = 0;
        for(int i=n-1;i>=0; --i) {
          if (v[i] == '#') {
            if (i<n-1&&v[i+1]=='A' || i>0&&v[i-1]=='A')
              continue;
            v[i] = c;
            f = 1;
            break;
          }
        }
        if (!f) {
          REP(i,n) {
            if (v[i] == '#') {
              v[i] = c;
              break;
            }
          }
        }
      } else if (c=='C') {
        bool f = 0;
        REP(i,n) {
          if (v[i] != '#') {
            if (i<n-1 && v[i+1]=='#') {
              v[i+1] = c;
              f = 1;
              break;
            }
            
            if (i>0&&v[i-1]=='#') {
              v[i-1] = c;
              f = 1;
              break;
            }
          }
        }
        if (!f) {
          if (n%2)
            v[(n+1)/2-1] = c;
          else
            v[n/2] = c;
        }
      } else {
        vector<int> dst(n,INF);
        REP(i,n) REP(j,n)
          if (v[j] != '#')
            dst[i] = min(dst[i], abs(i-j));
        int ma = 0;
        int p = 0;
        REP(i,n) {
          if (v[i] == '#' &&ma < dst[i]) {
            ma = dst[i];
            p = i;
          }
        }
        v[p] = c;
      }
       // REP(i,n)
       //   cout << v[i];
       // cout << endl;

    }
    REP(i,n)
      cout << v[i];
    cout << endl;
  }
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;

#define MAX 110
typedef pair<int, int> P;
int n, m;
char chair[MAX];
bool isZero;

bool isCanSit(int x){
  if(chair[x] == '#') return true;
  return false;
}

void A(){
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'A';
      isZero = false;
      return;
    }
  }
}

bool isNext(int x){
  if(chair[x-1] == 'A' || chair[x+1] == 'A') return true;
  return false;
}

void B(){
  for(int i = n-1 ; i >= 0 ; i--){
    if(isCanSit(i) && !isNext(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
  
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
}

void C(){
  if(isZero){
    if(n % 2 == 1) chair[n/2] = 'C';
    else chair[n/2] = 'C';
    isZero = false;
    return;
  }
  
  for(int i = 0 ; i < n ; i++){
    if(!isCanSit(i)){
      if(isCanSit(i+1)){
	chair[i+1] = 'C';
	isZero = false;
	return;
      }
      else if(isCanSit(i-1)){
	chair[i-1] = 'C';
	isZero = false;
	return;
      }
    }
  }
}

bool DcanSitNoneNext(int x){
  if(x == n-1){
    if(chair[x-1] == '#') return true;
  }
  if(x == 0){
    if(chair[x+1] == '#') return true;
 }  
  if(chair[x-1] == '#' && chair[x+1] == '#') return true;
  return false;
}

int calcDisD(int x){
  int ret, cnt = 0;
  for(int i = x-1 ; i >= 0 ; i--){ // left
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = cnt;
  cnt = 0;
  
  for(int i = x+1 ; i < n ; i++){ // right
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = max(ret, cnt);
  return ret;
}

void D(){
  if(isZero){
    chair[0] = 'D';
    isZero = false;
    return;
  }
  
  int sit;
  int dis[MAX];
  fill(dis, dis+MAX, MAX);
  for(int i = 0 ; i < n ; i++){
    if(chair[i] != '#'){
      for(int j = 0 ; j < n ; j++){
	dis[j] = min(dis[j], abs(i-j));
      }
    }
  }  
  int d = 0;
  for(int i = 0 ; i < n ; i++){
    if(dis[i] > d){
      sit = i;
      d = dis[i];
    }
  }
  chair[sit] = 'D';
  return;
}
  
void init(){
  fill(chair, chair+MAX, '#');
  isZero = true;
}

void display(){
  for(int i = 0 ; i < n ; i++){
    cout << chair[i];
  }
  cout << endl;
}

int main(){
  char p;
  while(cin >> n >> m){
    if(n == 0 && m == 0) break;
    init();
    for(int i = 0 ; i < m ; i++){
      cin >> p;
      if(p == 'A') A();
      if(p == 'B') B();
      if(p == 'C') C();
      if(p == 'D') D();
      display();
    }
    display();
  }
  return 0;
}