#include<iostream>
using namespace std;

int main(){
    string A,B;
    cin>>A>>B;
    bool ng=(A.length()<=5)&&(B.length()<=5)||!(A.length()>1&&A[0]=='0')||!(B.length()>1&&B[0]=='0');
    bool sizeng=true;
    for(int i=0; i<A.length(); i++){
        if(A[i]<'0'||A[i]>'9')ng=false;
        if(sizeng)sizeng&=A[i]<=i+1;
    }
    for(int i=0; i<B.length(); i++){
        if(B[i]<'0'||B[i]>'9')ng=false;
        if(sizeng)sizeng&=B[i]<=i+1;
    }
    cout<<((ng&&sizeng)?("OK"):("NG"))<<endl;
    return 0;
}