Pascal :

var n,m,i,j,k,l:longint; s:array [1..10000000] of longint;
begin
    readln(n,m);     k:=0;
    for i:=1 to n do
    begin
        read(k);
        for j:=1 to k do begin read(l); s[l]:=s[l]+1;  end;
        readln;
    end;
    k:=1;
    for i:=1 to 100000 do if s[i]>s[k] then k:=i;
    if s[k]>m then writeln(k);
end.