#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 (int i = (int)a; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF 1000000000
#define PI 3.14159265359
#define EPS 1e-12

int main(void)
{
  string a, b;
  cin >> a >> b;

  // 英語が含まれるか
  REP(i, a.size()) {
    if(a[i] < '0' || a[i] > '9') {
      cout << "NG" << endl;
      return 0;
    }
  }
  REP(i, b.size()) {
    if(b[i] < '0' || b[i] > '9') {
      cout << "NG" << endl;
      return 0;
    }
  }
  //leading zero
  if((a.size() != 1 && a[0] == '0') || (b.size() != 1 && b[0] == '0')) {
    cout << "NG" << endl;
    return 0;
  }
  // > 12345
  if(a.size() == 5) {
    REP(i, 5) {
      if((a[i] - '0') > i+1) {
        cout << "NG" << endl;
        return 0;
      }
    }
  }
  if(b.size() == 5) {
    REP(i, 5) {
      if((b[i] - '0') > i+1) {
        cout << "NG" << endl;
        return 0;
      }
    }
  }

  cout << "OK" << endl;
  return 0;
}