c++
#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s1,s2,s3,s4;cin>>s1>>s2>>s3;
    if(s1!="ABC"&&s2!="ABC"&&s3!="ABC") 
    {
        cout<<"ABC";
    }
    else if(s1!="ARC"&&s2!="ARC"&&s3!="ARC")
    {
        cout<<"ARC";
    }
    else if(s1!="AHC"&&s2!="AHC"&&s3!="AHC")
    {
        cout<<"AHC";
    }
    else if(s1!="AGC"&&s2!="AGC"&&s3!="AGC")
    {
        cout<<"AGC";
    }
    return 0;
}