const
  inf='leader.in';
  ouf='leadaer.out';
var
  a:array[1..10000] of longint;
  n,m,i,k,ans,max:longint;
procedure nasha(l,r:longint);
  var
    tmp,i,j,mid:longint;
  begin
    i:=l;
    j:=r;
    mid:=a[(i+j)div 2];
    repeat
      while a[i]<mid do inc(i);
      while a[j]>mid do dec(j);
      if i<=j then
        begin
          tmp:=a[i];a[i]:=a[j];a[j]:=tmp;
          inc(i);
          dec(j);
        end;
    until i>j;
    if l<j then nasha(l,j);
    if i<r then nasha(i,r);
  end;

begin
  assign(input,inf); reset(input);
  assign(output,ouf); rewrite(output);
  readln(n,m);
  for i:=1 to m do read(a[i]);
  nasha(1,m);
  k:=1;max:=1;ans:=a[1];
  for i:=2 to m do begin
    if a[i]=a[i-1] then
      begin
        inc(k);
        if max<k then begin max:=k; ans:=a[i];end;
      end
    else k:=1;
  end;
  if max > m div 2 then writeln(ans)
  else writeln(-1);
  close(input); close(output);
end.