program compconex;
var a:array[1..10000,1..10000] of byte;
    v:array[1..10000] of byte;
    n,m,i,j:longint;
    c:int64;
    f,g:text;
procedure citire;
var i,j,k:integer;
  begin
    assign(f,'dfs.in');
    assign(g,'dfs.out');
    reset(f);
    rewrite(g);
    readln(f,n,m);
    for k:=1 to m do
      begin
        readln(f,i,j);
        a[i,j]:=1;
        a[j,i]:=1;
      end;
    close(f);
  end;
begin
  citire;
  i:=1;
  c:=0;
  while i<=n do
    begin
     if v[i]=0 then
      begin
        for j:=1 to n do
          if a[i,j]=1 then
                      v[j]:=1;
        i:=i+1;
        c:=c+1;
      end
      else
      i:=i+1;
    end;
  writeln(g,c);
  close(g);
end.