#include<bits/stdc++.h> 
using namespace std;
namespace Mikazuki_Munechika {
	typedef long long ll;
	typedef double db;
	#define lowbit(a) a&-a
	#define pii pair<int , int>
	#define rep(i , a , n ) for(int i (a); i <= n ; i++)
	#define per(i , a , n ) for(int i (n); i >= a ; i--)
	#define aper(i , a) for(auto i : a)
	#define pb push_back
	#define mp make_pair
	#define rs(x) x<<1|1
	#define ls(x) x<<1
	#define fi first
	#define se second
	#define YES puts("Yes")
	#define NO puts("No")
	#define gc getchar
	#define pc putchar
	#define size(x) (int)x.size()
	#define all(x) x.begin(),x.end()
	#define vreturn return (void)
	#define endl '\n'
	#define doret(x) {x;return;}
	#define brk(x) {x;break;}
	#define ctn(x) {x;continue;}
    #define reset(x, y) memset(x, y, sizeof(x))
	#define BUG(x) cerr << #x << " = " << (x) << endl
	#define BUGP(x) cout << #x << " = " << (x).first << ", " << (x).second << endl
	int _;
    ll __;
	template<typename T , const T mod>
	struct mint {
		int v = 0;
		mint(int _v = 0) : v(_v) {}
		mint &operator += (const mint &X) { return (v += X.v) >= mod ? v -= mod : v, *this; }
	        mint &operator -= (const mint &X) { return (v += mod - X.v) >= mod ? v -= mod : v, *this; }
	        mint &operator *= (const mint &X) { return v = 1ll * v * X.v % mod, *this; }
	        mint &operator /= (const mint &X) { return *this *= X.inv(); }
	        mint qpow(int y) const { mint res = 1, x = *this; while (y) { if (y & 1) res *= x; x *= x; y >>= 1; } return res; }
	        mint inv() const { return qpow(mod - 2); }
	        friend mint operator + (const mint &A, const mint &B) { return mint(A) += B; }
	        friend mint operator - (const mint &A, const mint &B) { return mint(A) -= B; }
	        friend mint operator * (const mint &A, const mint &B) { return mint(A) *= B; }
	        friend mint operator / (const mint &A, const mint &B) { return mint(A) /= B; }
	};
	typedef mint<int , 998244353> mi9; 
	typedef mint<int , 1000000007> mi1;
	template<typename T>inline T _gcd(T x, T y) {return y ? _gcd(y, x % y) : x;}
	template<typename T>inline T abs(T x) {return x > 0 ? x : -x;}
	template<typename T>inline T _abs(T x){return x = x > 0 ? x : -x;}
	template<typename T>inline T _max(T &x, T y) {return x = x > y ? x : y;}
	template<typename T>inline T _min(T &x, T y) {return x = x > y ? y : x;}
	template<typename T>inline void _ck(T x) {vreturn (x ? YES : NO);}
	template<typename T>inline T read(T &x) {T ch = gc(), ans = 0, fl = 1;for (; !isdigit(ch) ; ch = gc())if (ch == '-')fl = -1;for (; isdigit(ch) ; ch = gc())ans = (ans << 1) + (ans << 3) + (ch ^ 48);return x = fl * ans;}
	template<typename T, typename ...Args>inline void read(T &x, Args &...args) {read(x);read(args...);}
	template<typename T>inline void write(T x) {if(x < 0 ) {pc('-');x = -x;}static int sta[35];int top = 0;do {sta[top++] = x % 10, x /= 10;} while (x);while (top)pc(sta[--top] + 48);pc(' ');return ;}
	template<typename T, typename ...Args>inline void write(T x, Args ...args) {write(x);write(args...);return ;}
	template<typename T, typename ...Args>inline void write_(T x) {write(x);puts("");return ;}
	template<typename T, typename ...Args>inline void write_(T x, Args ...args) {write(x);write(args...);puts("");return ;}
	const int N6 = 1000100;
	const int N5 = 100010;
	const int _N5 = 500010;
	const int _N6 = 5000100;
} using namespace Mikazuki_Munechika;

char ch[N6];

int A(int a , int b , int c){
	if(!a && (!b || !c)){
		return -1;
	}
	else if(!a){
		return A(a + 1 , b - 1 , c - 1);
	}else if(b && c){
		return A(a + 1 , b - 1 , c - 1);
	}else if(b){
		return A(a - 1 , b - 1 , c + 1);
	}else if(c){
		return A(a - 1 , b + 1 , c - 1);
	}else return a;
}

void solve() {
	map<char,int> pm;
	int n;

	while(~scanf("%d" , &n)){
		pm.clear();
		cin >> (ch + 1);
		rep(i ,1 , n){
			pm[ch[i]] ++;
		}
		// cerr << pm['A'] << pm['B'] << pm['C'];
		int ansa = A(pm['A'] , pm['B'] , pm['C']),
			ansb = A(pm['B'] , pm['A'] , pm['C']),
			ansc = A(pm['C'] , pm['A'] , pm['B']);
		if(ansa == ansb && ansb == ansc) {
			puts("N");
			continue;
		}
		pair<ll,char> se[] = {{ansa , 'A'} , {ansb , 'B'} , {ansc , 'C'}};
		sort(se , se + 3);
		cout << se[2].second << "\n";
	}
}

// #define LOCAL
signed main() {
#ifdef LOCAL
    freopen("snow.in", "r", stdin);
    freopen("snow.out", "w", stdout);
#endif
    // int tt = read<int>(_);
    // init();
    clock_t c1 = clock();
    // while (1) {
        solve();
    // }
    cerr << "Time:" << clock() - c1 << "ms" << endl;
    return 0;
}