#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define cint(d) scanf("%d", &d)
#define cint2(a, b) scanf("%d %d", &a, &b)
#define cint3(a, b, c) scanf("%d %d %d", &a, &b, &c)
#define cint4(a, b, c, d) scanf("%d %d %d %d", &a, &b, &c, &d)

#define clong(d) scanf("%lld", &d)
#define clong2(a, b) scanf("%lld %lld", &a, &b)
#define clong3(a, b, c) scanf("%lld %lld %lld", &a, &b, &c)
#define clong4(a, b, c, d) scanf("%lld %lld %lld %lld", &a, &b, &c, &d)

#define foreach(v, c) for(__typeof( (c).begin()) v = (c).begin();  v != (c).end(); ++v)
#define revforeach(v, c) for(__typeof( (c).rbegin()) v = (c).rbegin();  v != (c).rend(); ++v)
#define ALL(v) (v).begin(), (v).end()

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second

typedef long long int slong;
typedef pair<int, int> pii;
typedef pair<slong, slong> pll;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
typedef set<int>::iterator sit;
typedef map<int,int>::iterator mit;
typedef vector<int>::iterator vit;

#ifdef VSP4 
    #include "debug.h"    
#else
    #define debug(args...)                  // Just strip off all debug tokens
#endif

const int MOD = 1000000007;
#define MODSET(d) if ((d) >= MOD) d %= MOD;
#define MODNEGSET(d) if ((d) < 0) d = ((d % MOD) + MOD) % MOD;
#define MODADDSET(d) if ((d) >= MOD) d -= MOD;
#define MODADDWHILESET(d) while ((d) >= MOD) d -= MOD;

const int MAXN = 100;
const int SQRTN = 550;
const int LOGN = 60;
const int INT_INFINITY = 1001001001;
const int LIMIT = 1e6;

const slong LONG_INFINITY = 1001001001001001001ll;
const slong LONG_LIMIT = 200100100100101ll;

const double DOUBLE_INFINITY = 1e16;

int N, R, O, Y, G, B, V;

int main()
{
	#ifdef VSP4
		freopen("input.txt", "r", stdin);
		freopen("output.txt", "w", stdout);
	#endif
	
	cout.tie(0);
	cin.tie(0);
	
	int t, T, i, j;
	
    cin >> T;
	
    for (t = 1; t <= T; t++)
	{
		cin >> N >> R >> O >> Y >> G >> B >> V;
		
		vector<pair<int, char> > data;
		
		data.pb(mp(R, 'R'));
		data.pb(mp(Y, 'Y'));
		data.pb(mp(B, 'B'));
		
		sort(ALL(data), greater<pair<int, char> >());
		
		cout << "Case #" << t << ": ";
		
		if (data[0].fi == 1)
		{
			for (i = 0; i < 3; i++)
			{
				if (data[i].fi)
				{
					cout << data[i].se;
				}
			}
		}
		else
		{
			if (data[0].fi <= (data[1].fi + data[2].fi))
			{
				vector<pair<int, char> > back = data;
				
				int extra = (data[1].fi + data[2].fi) - data[0].fi;
				
				int a, b, c;
				a = b = c = 0;
				
				for (i = 0; i < extra; i++)
				{
					a++;
					b++;
					c++;
					cout << data[0].se << data[1].se << data[2].se;
				}
				
				data[1].fi -= extra;
				data[2].fi -= extra;
				
				for (i = 0; i < data[1].fi; i++)
				{
					a++;
					b++;
					cout << data[0].se << data[1].se;
				}
				
				for (i = 0; i < data[2].fi; i++)
				{
					a++;
					c++;
					cout << data[0].se << data[2].se;
				}
				
				assert(a == back[0].fi);	
				assert(b == back[1].fi);	
				assert(c == back[2].fi);		
			}
			else
			{
				cout << "IMPOSSIBLE";
			}
		}
		
		cout << endl;
	}
	
	return 0;
}