为什么不对呢?明明那么多人AC............
program rq343(input,output);
  var a,b,i,n,m,t:integer;
      s:array [1..1000] of boolean;
  begin
    readln(n,m);
    t:=0;
    for i:=1 to 1000 do
      s[i]:=false;
    for i:=1 to m do
      begin
        readln(a,b);
        if not s[a] then begin inc(t);
                               s[a]:=true;
                             end;
        if not s[b] then begin inc(t);
                               s[b]:=true;
                         end;
      end;
    write(t);
  end.