#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

int cross[110];

int main() {
	int a,b;
	while(cin>>a>>b){
		if(a){
			cross[a]++;
			cross[b]++;
		}else{
			int i=0;
			if(cross[1]%2==1&&cross[2]%2==1){
				for(i=3;i<101;i++){
					if(cross[i]%2==1)break;
				}
			}
			if(i==101)cout<<"OK"<<endl;
			else cout<<"NG"<<endl;
			memset(cross,0,sizeof(cross));
		}
	}
	return 0;
}