#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <utility>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <map>
#include <set>
#include <queue>
 
using namespace std;
 
#define pb(n)	push_back(n)
#define mp(n,m) make_pair(n,m)
#define fi 	first
#define se 	second
#define all(r) (r).begin(),(r).end()

#define rep(i,n) for(int i=0; i<(n); i++)
#define repc(i,a,b) for(int i=(a); i<=(b); i++)

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
const int IMAX=((1<<30)-1)*2+1;
const double EPS=1e-10;
//int mod=1000000007;




int main(){
	int a,b;
	vi v(101,0);
	while(cin>>a>>b){
		v[a]++;
		v[b]++;
		if(a==0){
			bool f=true;
			if(v[1]%2==0||v[2]%2==0){
				f=false;
			}
			for(int i=3; i<101; i++){
				if(v[i]%2==1||!f){
					f=false;
					break;
				}
			}
			cout<<(f?"OK":"NG")<<endl;
			for(int i=0; i<101; i++){
				v[i]=0;
			}
		}
	}
}