#include<iostream>#include<cstdio>using namespace std;int main(){    for(;;){        int a,b,x = 0;        int field[100] = {0};        for(;;){            if(scanf("%d %d",&a,&b) == EOF){goto jump;}            if(!a && !b){break;}            field[a]++;            field[b]++;        }        for(int i=0; i<100; i++){            if(field[i]%2 == 1){x++;}        }        if(x == 2){cout <<"OK"<<endl;}        else{cout <<"NG"<<endl;}    }    jump:;    return 0;}