#include<bits/stdc++.h>
#include<cmath>
#define ll long long
#define For(i,a,b) for(int i=a;i<=b;i++)
#define Rof(i,a,b) for(int i=a;i>=b;i--)
#define N 100010

using namespace std;
int b[3];

ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}


int main()
{
    //freopen("snow.in","r",stdin);
    //freopen("snow.out","w",stdout);
    int n;
    while(cin>>n){
    	b[0]=b[1]=b[2]=0;
    	For(i,1,n){
    		char s;
    		cin>>s;
    		b[s-'A']++;
		}
		int x=(b[0]%2==b[1]%2?b[0]+b[1]-b[2]:0x3f3f3f3f),
			y=(b[0]%2==b[2]%2?b[0]+b[2]-b[1]:0x3f3f3f3f),
			z=(b[2]%2==b[1]%2?b[2]+b[1]-b[0]:0x3f3f3f3f);
		int mn=min(x,min(y,z));
		if((mn==x)+(mn==y)+(mn==z)>1) cout<<"N"<<endl;
		else cout<<(x==mn?"C":(y==mn?"B":"A"))<<endl;
	}
    return 0;
}