#include <iostream>
#include <cstring>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <map>
#include <cmath>
#include <queue>
#include <utility>
#include <functional>
#include <deque>
#include <cctype>
#include <stack>
#include <bitset>

using ll = long long;
using namespace std;
typedef unsigned long long ull;
typedef pair<ll, ll>P;

ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a%b);
}
ll lcm(ll a, ll b) {
	ll g = gcd(a, b);
	return a / g * b;
}

const ll mod = 1000000007;
const ll INF = 1 << 30;
const ll INF2 = 9000000000000000000LL;
bool fl = true;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
string abc = "abcdefghijklmnopqrstuvwxyz";
struct edge { ll to, cost; };
struct edge1 { ll from, to, cost; };
double pai = 3.141592653589793;

int main() {
	string s, t;
	cin >> s >> t;
	if (s[0] == '0'&&s.size()!=1 || t[0] == '0'&&t.size()!=1) {
		cout << "NG" << endl;
		exit(0);
	}
	for (int i = 1;i < s.size();i++) {
		if (s[i] != '1'&&s[i] != '2'&&s[i] != '3'&&s[i] != '4'&&s[i] != '5'&&s[i] != '6'&&s[i] != '7'&&s[i] != '8'&&s[i] != '9'&&s[i] != '0') {
			cout << "NG" << endl;
			exit(0);
		}
	}
	for (int i = 1;i < t.size();i++) {
		if (t[i] != '1'&&t[i] != '2'&&t[i] != '3'&&t[i] != '4'&&t[i] != '5'&&t[i] != '6'&&t[i] != '7'&&t[i] != '8'&&t[i] != '9'&&t[i] != '0') {
			cout << "NG" << endl;
			exit(0);
		}
	}
	cout << "OK" << endl;

}