#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <queue>
#include <sstream>
#include <climits>
#include <cmath>
#include <functional>
#include <map>
#include <stack>
using namespace std;
#define M_PI 3.141592
#define FOR(i,n) for(int i=0;i<(int)n;i++)
#define FORI(i,k,n) for(int i=k;i<(int)n;i++)
#define toRad 2.0*M_PI/360.0
#define inin(x) int x;cin>>x;
#define all(x) x.begin(),x.end()
#define debug(x) cout<<#x<<" :"<<x<<endl;
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define EPS 1e-12
#define pri_max 60000
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };

/* 
bool memo[pri_max] = {};
vector<int> pri;
void calc()
{
	for (int i = 2; i < pri_max; i++)
	{
		if (memo[i] == false)
		{
			pri.push_back(i);
			for (int l = i; l < pri_max; l += i)
			{
				memo[l] = true;
			}
		}
	}
}*/
double len(pdd a, pdd b)
{
	return sqrt((b.first - a.first)*(b.first - a.first) + (b.second - a.second)*(b.second - a.second));
}



int hoge(int p,vector< pii > v)
{
	if (p == 2&&v.size()==0)
	{
		return 1;
	}
	if (v.size() == 0)return 0;
	int ans = 0;
	for (int i = 0; i < v.size(); i++)
	{
		if (ans)return ans;
		if (v[i].first == p || v[i].second == p)
		{
			vector<pii> t(v);
			t.erase(t.begin() + i);
			ans += hoge(p == v[i].first ? v[i].second : v[i].first, t);
		}
	}
	return ans;

}


int main()
{
	while (1)
	{
		vector< pii > way;
		pii w;
		while (cin >> w.first >> w.second&&w.first)
		{
			way.push_back(w);
		}
		if (way.size() == 0)break;
		cout << (hoge(1, way) ? "OK" : "NG") << endl;
	}
}