#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define whole(x) (x).begin(),(x).end()
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
using P = pair<int, int>;
#define debug(var) cerr << "[" << #var << "] " << var << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
const ll mod = 1000000007;
const int dx[] = {-1,0,1,0};
const int dy[] = {0,-1,0,1};


int main(){
    int n;
    cin >> n;
    string ans = "AGC";
    if (n<1200) ans = "ABC";
    else if (n<2800) ans = "ARC";
    
    cout << ans << endl;
    return 0;
}

/*
Author : Devil088
*/
#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define sep cout<<"\n";
#define Yes cout<<"Yes\n";
#define No cout<<"No\n";
#define YES cout<<"YES\n";
#define NO cout<<"NO\n";

inline string shift(string s){
	int n = s.length();
	string r = "";
	r+=s[n-1];
	for(int i=0;i<n-1;i++)r+=s[i];
	return r;
}

int main(){
	int n;
	cin>>n;
	
	if(n<1200){
		cout<<"ABC\n";
	}else if(n<2800){
		cout<<"ARC\n";
	}else cout<<"AGC\n";
}
/*
uday
adyu
7 46
45 6
*/

