program teeem;

var f,g:text;
a:array[1..10000,1..10000] of integer;
v,viz,pred:array[1..10000] of integer;
i,j,sf,st,n,m,c,x,t,k:longint;
ok:boolean;
procedure df(nod:longint);
var k:longint;
begin
for k:=1 to n do
   if (a[nod,k]=1)and(viz[k]=0) then
      begin
      pred[k]:=nod;
      viz[k]:=1;
      df(k);
      end;
end;
  begin
  assign(f,'dfs.in'); reset(f);
  assign(g,'dfs.out'); rewrite(g);
    readln(f,n,m);
    c:=0;
      for i:=1 to n do
         for j:=1 to n do
           a[i,j]:=0;
      for i:=1 to m do
      begin
         readln(f,k,t);
         a[k,t]:=1;
         a[t,k]:=1;
      end;
      viz[1]:=0;
       for i:=1 to n do
         begin
         if viz[i]=0 then
         begin
         df(i);
         c:=c+1;
         end;
         end;
       write(g,c);
  close(f);
  close(g);
  end.