1 const
 2         maxn=410;
 3 var
 4         s:array[0..maxn]of longint;
 5         n,m:longint;
 6
 7 procedure init;
 8 var
 9         i,x:longint;
10 begin
11         read(n,m);
12         for i:=1 to 3*m+1 do
13           begin
14             read(x);
15             inc(s[x]);
16           end;
17 end;
18
19 function dfs(x:longint):boolean;
20 var
21         i,k:longint;
22 begin
23         while (s[x]=0) and (x<=n) do
24           inc(x);
25         if x>n then exit(true);
26         k:=s[x]mod 3;
27         for i:=s[x]div 3 to s[x]div 3 do
28           begin
29             dec(s[x+1],k);
30             dec(s[x+2],k);
31             if (s[x+1]>=0) and (s[x+2]>=0) then
32             if dfs(x+1) then
33             begin
34               inc(s[x+1],k);
35               inc(s[x+2],k);
36               exit(true);
37             end;
38             inc(s[x+1],k);
39             inc(s[x+2],k);
40             inc(k,3);
41           end;
42         exit(false);
43 end;
44
45 procedure work;
46 var
47         i,j:longint;
48         flag:boolean;
49 begin
50         flag:=false;
51         for i:=1 to n do
52           begin
53             inc(s[i]);
54             for j:=1 to n do
55               if s[j]>1 then
56               begin
57                 dec(s[j],2);
58                 if dfs(1) then
59                 begin
60                   inc(s[j],2);
61                   if flag=false then write(i)
62                   else write(' ',i);
63                   flag:=true;
64                   break;
65                 end;
66                 inc(s[j],2);
67               end;
68             dec(s[i]);
69           end;
70         if flag=false then write('NO');
71 end;
72
73 begin
74         init;
75         work;
76 end.