#include <iostream>
#include <cstdio>
#include <vector>
#include <list>
#include <cmath>
#include <fstream>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <complex>
#include <iterator>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <stack>
#include <climits>
#include <deque>
#include <bitset>
#include <cassert>
#include <ctime>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
const int dy[]={-1,0,1,0},dx[]={0,1,0,-1};
// adjust problem by problem
const double EPS=1e-8;
const double PI=acos(-1.0);
#ifdef __GNUC__
int popcount(int n){return __builtin_popcount(n);}
int popcount(ll n){return __builtin_popcountll(n);}
#endif
#ifndef __GNUC__
template<class T> int popcount(T n){int cnt=0;while(n){if(n%2)cnt++;n/=2;}return cnt;}
#endif
template<class T>int SIZE(T a){return a.size();}
template<class T>string IntToString(T num){string res;stringstream ss;ss<<num;return ss.str();}
template<class T>T StringToInt(string str){T res=0;for(int i=0;i<SIZE(str);i++)res=(res*10+str[i]-'0');return res;}
template<class T>T gcd(T a,T b){if(b==0)return a;return gcd(b,a%b);}
template<class T>T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> void PrintSeq(T &a,int sz){for(int i=0;i<sz;i++){cout<<a[i];if(sz==i+1)cout<<endl;else cout<<' ';}}
bool EQ(double a,double b){return abs(a-b)<EPS;}
void fastStream(){cin.tie(0);std::ios_base::sync_with_stdio(0);}
vector<string> split(string str,char del){
  vector<string> res;
  for(int i=0,s=0;i<SIZE(str);i++){
    if(str[i]==del){if(i-s!=0)res.push_back(str.substr(s,i-s));s=i+1;}
    else if(i==SIZE(str)-1){res.push_back(str.substr(s));}
  }
  return res;
}

int maxv;
int N;
int d[303];
bool used[304];
int main(){

  while(cin>>maxv&&maxv){
    memset(used,0,sizeof(used));
    memset(d,0,sizeof(d));
    cin>>N;
    for(int i=1;i<=N;i++)cin>>d[i];
    N+=2;
    queue<int> q;
    q.push(0);
    used[0]=true;
    while(q.size()){
      int now=q.front();q.pop();
      for(int i=1;i<=maxv;i++){
        int to=min(N-1,now+i);
        if(used[to])continue;
        if(d[to]>0){
          to=min(N-1,to+d[to]);
          if(!used[to]){
            q.push(to);
            used[to]=true;
          }
        }
        else if(d[to]<0){
          to=max(0,to+d[to]);
          if(!used[to]){
            q.push(to);
            used[to]=true;
          }
        }
        else{
          used[to]=true;
          q.push(to);
        }
      }
    }
    vector<int> cand;
    for(int i=0;i<N-1;i++)if(used[i])cand.push_back(i);
    for(int ite=0;ite<(int)cand.size();ite++){
      memset(used,0,sizeof(used));
      queue<int> q;
      q.push(cand[ite]);
      used[cand[ite]]=true;
      while(q.size()){
        int now=q.front();q.pop();
        for(int i=1;i<=maxv;i++){
          int to=min(N-1,now+i);
          if(d[to]>0){
            to=min(N-1,to+d[to]);
            if(!used[to]){
              q.push(to);
              used[to]=true;
            }
          }
          else if(d[to]<0){
            to=max(0,to+d[to]);
            if(!used[to]){
              q.push(to);
              used[to]=true;
            }
          }
          else{
            if(used[to])continue;
            used[to]=true;
            q.push(to);
          }
        }
      }
      // テ」ツつエテ」ツδシテ」ツδォテ」ツ?クテ・ツ按ーテゥツ?氾」ツ?ァテ」ツ?催」ツ?ェテ」ツ??」ツδ妥」ツつソテ」ツδシテ」ツδウテ」ツ?古・ツュツ佚・ツ慊ィ
      if(!used[N-1]){
        cout<<"NG"<<endl;
        break;
      }
    }
    if(used[N-1])cout<<"OK"<<endl;
  }
  
  return 0;
}

Measured memory_bytes: 1220