#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <utility>
#include <functional>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
using namespace std;
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string toStr(T x) { ostringstream sout; sout << x; return sout.str();}
typedef vector<int> vi;
typedef vector<vi>  vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,n) FOR(i,0,(n)-1)
const double EPS = 1e-12;
const double PI = acos(-1.0);
const int INF = INT_MAX/10;

int main() {
	int a, b;
	vi cross(100+1);
	while(cin >> a >> b) {
		if(a|b) {
			cross[a]++;
			cross[b]++;
		} else {
			int count = 0;
			bool ok = true;
			if(cross[1] != 1 || cross[2] != 1) {
				ok = false;
			}
			FOR(i, 3, 100) {
				if(cross[i]%2) {
					ok = false;
					break;
				}
			}

			cout << (ok ? "OK" : "NG") << endl;

			REP(i, 100+1) {
				cross[i] = 0;
			}
		}
	}
}