#include <iostream>
#include <algorithm>
#include <string>

void solve() {
    for (int i = 0; i < 2; ++i) {
        std::string s;
        std::cin >> s;

        if (s == "0") continue;

        if (s.front() == '0') {
            std::cout << "NG" << std::endl;
            return;
        }

        for (char c : s) {
            if (!std::isdigit(c)) {
                std::cout << "NG" << std::endl;
                return;
            }
        }
    }

    std::cout << "OK" << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}