#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MP make_pair
#define PB push_back
#define MOD 1000000007
#define INF (1LL<<30)
#define LLINF (1LL<<60)
#define PI 3.14159265359
#define EPS 1e-12
#define int ll

int cnt[105];
signed main(void)
{
  int a, b;
  while(cin >> a >> b) {
    cnt[a-1]++;
    cnt[b-1]++;
    if(!a && !b) {
      bool flag = true;
      if(cnt[0]%2 == 0 || cnt[1]%2 == 0) flag = false;
      FOR(i, 2, 100) if(cnt[i]%2) flag = false;
      if(flag) cout << "OK" << endl;
      else cout << "NG" << endl;
      REP(i, 100) cnt[i] = 0;
    }
  }

  return 0;
}