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
		}
		chair := make([]string, n+1)
		for i := range chair {
			chair[i] = "#"
		}
		chair[n] = "Sentinel"
		for i := 0; i < m; i++ {
			scanner.Scan()
			switch who := scanner.Text(); who {
			case "A": // 左から眺めて行って空いている席があったら即座に座る
				for j := 0; j < n; j++ {
					if chair[j] == "#" {
						chair[j] = "A"
						break
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "B":
				flag := true
				// 右端からAの隣でない席を探していく
				for j := n-1; j > -1; j-- {
					if chair[j] == "#" && (j == 0 || chair[j-1] != "A") && chair[j+1] != "A" {
						flag = false
						chair[j] = "B"
						break
					}
				}
				// Aの隣しか空いていないので一番左端の空いている席に座る
				if flag {
					for j := 0; j < n; j++ {
						if chair[j] == "#" {
							chair[j] = "B"
							break
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "C":
				if i == 0 {
					chair[n/2] = "C" // 先客が誰もいないときは真ん中の椅子に座る
				} else {
					for j := 0; j < n; j++ { // 左から舐めて
						if chair[j] != "#" { // その席が空いていなくて
							if chair[j+1] == "#" { // 右隣が空いているなら座る
								chair[j+1] = "C"
								break
							} else if j != 0 && chair[j-1] == "#" { // 右隣が空いていないので左隣に座る
								chair[j-1] = "C"
								break
							}
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "D":
				distanceTable := make([]int ,n)
				for j := range distanceTable {
					distanceTable[j] = INF
				}
				for j:= 0; j < n; j++ {
					if chair[j] != "#" {
						for k := 0; k < n; k++ {
							distanceTable[k] = min(distanceTable[k], abs(j-k))
						}
					}
				}
				// log.Println("distanceTAble:", distanceTable)
				at := 0
				distance := 0
				for j := 0; j < n; j++ {
					if distance < distanceTable[j] {
						at = j
						distance = distanceTable[j]
					}
				}
				chair[at] = "D"
				// log.Println(chair)
				break // 次の人を読み込む
			}
		}
		fmt.Println(strings.Join(chair, ""))
	}
}

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

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

C++: #include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

int chairs[110];
int n,m;

void fa(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=1;
			return;
		}
	}
}

void fb(){
	int i;
	for(i=n-1;i>=0;i++){
		if(chairs[i]==0&&(i==n-1||chairs[i+1]!=1)&&(i==0||chairs[i-1]!=1)){
			chairs[i]=2;
			return;
		}
	}
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=2;
			return;
		}
	}
}

void fc(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0)continue;
		if(i!=n-1&&chairs[i+1]==0){
			chairs[i+1]=3;
			return;
		}
		if(i!=0&&chairs[i-1]==0){
			chairs[i-1]=3;
			return;
		}
	}
	if(n%2==0){
		chairs[i/2+1]=3;
		return;
	}else{
		chairs[(i+1)/2]=3;
		return;
	}
}

void fd(){
	int i,j;
	int c=0,d=0,dd;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			for(j=1;i-j>=0;j++){
				if(chairs[i-j]!=0)break;
			}
			if(i-j<0)j=n;
			dd=j;
			for(j=1;i+j<n;j++){
				if(chairs[i+j]!=0)break;
			}
			if(i+j==n)j=n;
			chmin(dd,j);
			if(d<dd){
				c=i;
				d=dd;
			}
		}
	}
	chairs[c]=4;
	return;
}

int main() {
	while(cin>>n>>m){
		int i;
		string str;
		for(i=0;i<n;i++)chairs[i]=0;
		for(i=0;i<m;i++){
			cin>>str;
			if(str[0]=='A')fa();
			if(str[0]=='B')fb();
			if(str[0]=='C')fc();
			if(str[0]=='D')fd();
		}
		for(i=0;i<n;i++){
			if(chairs[i]==0)cout<<"#";
			else if(chairs[i]==1)cout<<"A";
			else if(chairs[i]==2)cout<<"B";
			else if(chairs[i]==3)cout<<"C";
			else if(chairs[i]==4)cout<<"D";
		}
		cout<<endl;
	}
	return 0;
}

C++: #include <iostream>

using namespace std;

int main()
{
    while(1){
        int n,c=1;
        cin>>n;
        if (n==0)break;
        cout<<"Case "<<c<<": "<<n<<endl;
        c++;
        }
}

C++: #include <bits/stdc++.h>
using namespace std;

int A(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] == '#') return i;
  }
  return -1;
}

int B(const string &s) {
  for(int i = s.size()-1; i >= 0; --i) {
    bool a = i == 0 || s[i-1] != 'A';
    bool b = i+1 == s.size() || s[i+1] != 'A';
    if(a && b) return i;
  }
  return A(s);
}

int C(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] != '#') {
      if(i+1 < s.size() && s[i+1] == '#') return i+1;
      if(i && s[i-1] == '#') return i-1;
    }
  }
  return s.size()/2;
}

int D(const string &s) {
  int maxi = -1, pos = -1;
  for(int i = 0, j = -1; i <= s.size(); ++i) {
    if(i == s.size() || s[i] != '#') {
      if(i-j-1 > maxi) {
        maxi = i-j-1;
        pos = j+1;
      }
      j = i;
    }
  }
  if(maxi == s.size()) return A(s);
  return pos + (maxi-1)/2;
}

int main() {
  for(int n, m; cin >> n >> m && (n|m);) {
    string s(n, '#');
    while(m--) {
      char c;
      cin >> c;
      int pos;
      switch(c) {
      case 'A': pos = A(s); break;
      case 'B': pos = B(s); break;
      case 'C': pos = C(s); break;
      case 'D': pos = D(s); break;
      }
      s[pos] = c;
    }
    cout << s << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

int main()
{
	int n, m;
	while (scanf("%d %d", &n, &m), n + m){
		string str;
		str += "*";
		for (int i = 0; i < n; i++){
			str += "#";
		}
		for (int i = 0; i < m; i++){
			string t;
			cin >> t;
			if (t == "A"){
				int j = 1;
				while (str[j] != '#'){
					j++;
				}
				str[j] = 'A';
			}
			else if (t == "B"){
				bool f = false;
				for (int j = str.size(); j >= 0; j--){
					if (str[j] == '#' && str[j - 1] != 'A' && str[j + 1] != 'A'){
						str[j] = 'B';
						f = true;
						break;
					}
				}
				if (!f){
					int j = 1;
					while (str[j] != '#'){
						j++;
					}
					str[j] = 'B';
				}
			}
			else if (t == "C"){
				if (i == 0){
					if (n % 2 == 1){
						str[(n + 1) / 2] = 'C';
					}
					else {
						str[n / 2 + 1] = 'C';
					}
				}
				else {
					for (int j = 1; j < str.size(); j++){
						if (str[j] != '#'){
							if (str[j + 1] == '#'){
								str[j + 1] = 'C';
								break;
							}
							else if (str[j - 1] == '#'){
								str[j - 1] = 'C';
								break;
							}
						}
					}
				}
			}
			else {
				int maxd = -1, maxp;
				for (int j = str.size() - 1; j > 0; j--){
					if (str[j] != '#') continue;
					bool f = false, ff = false;
					for (int k = 1; k <= 100 && !f && !ff; k++){
						if (j - k >= 0){
							if (str[j - k] != '#'){
								if (k > maxd){
									maxd = k;
									maxp = j;
									f = true;
								}
							}
						}
						if (j + k <= str.size()){
							if (str[j + k] != '#'){
								if (k > maxd){
									maxd = k;
									maxp = j;
									ff = true;
								}
							}
						}
					}
				}
				str[maxp] = 'D';
			}
		}
		
		string res = str.substr(1);
		cout << res << endl;
	}
	
	return 0;
}