#include <iostream>

typedef long long ll;
typedef double lf;

#define DEBUG 1
struct IO
{
    #define MAXSIZE (1 << 20)
    #define isdigit(x) (x >= '0' && x <= '9')
    char buf[MAXSIZE], *p1, *p2;
    char pbuf[MAXSIZE], *pp;
    #if DEBUG
    #else
    IO() : p1(buf), p2(buf), pp(pbuf) {}
    ~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
    #endif
    #define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
    #define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')

    template <typename T>
    void Read(T &x)
    {
        #if DEBUG
        std::cin >> x;
        #else
        bool sign = 0; char ch = gc(); x = 0;
        for (; !isdigit(ch); ch = gc())
            if (ch == '-') sign = 1;
        for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
        if (sign) x = -x;
        #endif
    }
    void Read(char *s)
    {
        #if DEBUG
        std::cin >> s;
        #else
        char ch = gc();
        for (; blank(ch); ch = gc());
        for (; !blank(ch); ch = gc()) *s++ = ch;
        *s = 0;
        #endif
    }
    void Read(char &c) {for (c = gc(); blank(c); c = gc());}

    void Push(const char &c)
    {
        #if DEBUG
        putchar(c);
        #else
        if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
        *pp++ = c;
        #endif
    }
    template <typename T>
    void Write(T x)
    {
        if (x < 0) x = -x, Push('-');
        static T sta[35];
        int top = 0;
        do sta[top++] = x % 10, x /= 10; while (x);
        while (top) Push(sta[--top] ^ 48);
    }
    template <typename T>
    void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)

using namespace std;

const int MAXN = 1e4 + 10, N = 20;

pair <int, int> f[MAXN][MAXN];
inline pair <int, int> _F(int i, int j, int k, int x)
{
    int c[3] = {0}; c[1] = i ^ j ^ k ^ max(i, max(j, k)), c[2] = max(i, max(j, k));
    int res = f[c[1]][c[2]].first + x;
    int g = f[c[1]][c[2]].second;
    if (i == c[g]) g = 0;
    else if (j == c[g]) g = 1;
    else if (k == c[g]) g = 2;
    return make_pair(res, g);
}
inline pair <int, int> F(int i, int j, int k)
{
    int c0 = (i == 0) + (j == 0) + (k == 0);
    if (c0 == 2) return make_pair(0, (i ? 0 : (j ? 1 : 2)));
    pair <int, int> st[7]; int top = 0;
    if (j >= i && i) st[++top] = _F(0, j - i, k + i, i);
    if (i >= j && j) st[++top] = _F(i - j, 0, k + j, j);
    if (k >= i && i) st[++top] = _F(0, j + i, k - i, i);
    if (i >= k && k) st[++top] = _F(i - k, j + k, 0, k);
    if (k >= j && j) st[++top] = _F(i + j, 0, k - j, j);
    if (j >= k && k) st[++top] = _F(i + k, j - k, 0, k);
    auto res = st[1];
    for (int i = 2; i <= top; i++) res = min(res, st[i]);
    int cc[7], num = 0;
    for (int i = 1; i <= top; i++)
        if (res.first == st[i].first) cc[++num] = st[i].second;
    bool flag = 1;
    for (int i = 1; i < num; i++)
        if (cc[i] != cc[i + 1]) {flag = 0; break;}
    if (flag) return make_pair(res.first, cc[1]);
    else return make_pair(res.first, -1);
}

char str[MAXN];
int main()
{
    // freopen("C.out", "w", stdout);
    #if DEBUG
    #else
    ios::sync_with_stdio(0), cin.tie(0);
    #endif
    for (int tot = 1; tot <= N; tot++)
        for (int i = 0; i * 2 <= tot; i++)
        {
            int j = tot - i;
            if (i == 0) {f[i][j] = make_pair(0, 2); continue;}
            f[i][j] = F(1, i - 1, j - 1), f[i][j].first++;
            // cout << i << ' ' << j << " " << f[i][j].first << ' ' << f[i][j].second << "\n";
        }
    int n;
    while (cin >> n)
    {
        cin >> str + 1;
        int cnt[3] = {0};
        for (int i = 1; i <= n; i++)
            cnt[str[i] - 'A']++;
        auto res = F(cnt[0], cnt[1], cnt[2]);
        if (res.second == -1) cout << "N\n";
        else cout << (char)(res.second + 'A') << "\n";
    }
    return 0;
}