#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD % 1000000007
using namespace std;
typedef long long LL;
typedef vector<int> VI;


int main() {
	string a, b;
	cin >> a >> b;
	bool bo = true;
	REP(i, SZ(a)) if ('0' > a[i] || a[i] > '9' || SZ(a) > 4 && a[i] > '1' + i) bo = false;
	REP(i, SZ(b)) if ('0' > b[i] || b[i] > '9' || SZ(b) > 4 && b[i] > '1' + i) bo = false;
	if (SZ(a) > 1 && a[0] == '0' || SZ(b) > 1 && b[0] == '0') bo = false;
	if (bo) cout << "OK" << endl;
	else cout << "NG" << endl;
	return 0;
}