#include <bits/stdc++.h>
#define debugf(...) fprintf(stderr,__VA_ARGS__)
#ifdef ONLINE_JUDGE
#define fprintf(...) (1)
#endif
using namespace std;
constexpr int N=10007,INF{0x3F3F3F3F};
int n,a[N];
char s[N];
int cc[3];
int ans,as{INF};
inline int step(int a){
    // static int cnt[3];
    // memcpy(cnt,cc,sizeof cc);
    int b{cc[(a+1)%3]},c{cc[(a+2)%3]};
    a=cc[a];
    int dd(min(b,c)),ss{0};
    b-=dd,c-=dd;
    ss+=dd;
    if(c) swap(b,c);
    // printf("%d,%d\n",b,c);
    if(!b) return ss;
    ss+=(b>>1),b-=((b>>1)<<1);
    if(b) return INF;
    return ss;
}
inline bool mian(){
    if(scanf("%d%s",&n,s+1)==EOF) return false;
    cc[0]=cc[1]=cc[2]=0;
    for(int i{1};i<=n;++i) a[i]=s[i]-65,++cc[a[i]];
    ans=-1,as=INF;
    for(int i:{0,1,2}){
        int s{step(i)};
        // printf("step %c=%d\n","ABC"[i],s);
        if(s<as) ans=i,as=s;
        else if(s==as) ans=-1;
        // printf("ans=%d,as=%d\n",ans,as);
    }
    printf("%c\n","NABC"[ans+1]);
    return true;
}
signed main(){
    // freopen("snow.in","r",stdin);
    // freopen("snow.out","w",stdout);
    while(mian());return 0;}

/*
 CCCCAB
 AAABBB
 AACBB
 ABBB

 ABBBBBBBBB
*/