/*
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
*/


/**
 *    author:  otera    
**/
#include<iostream>
#include<string> 
#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<algorithm> 
#include<functional>
#include<iomanip>
#include<queue>
#include<deque>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

//#define int long long
typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf=1e9+7;
const ll INF=1LL<<60 ;
const ll mod=1e9+7 ;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define pb push_back
#define debug(x)  cerr << #x << " = " << (x) << endl;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

void solve() {
	int r; cin >> r;
    if(r < 1200) cout << "ABC\n";
    else if(r < 2800) cout << "ARC\n";
    else cout << "AGC\n";
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//int t; cin >> t; rep(i, t)solve();
	solve();
    return 0;
}