program p1;
var a:array[0..1000,0..1000] of 0..1;
    b:array[0..1000000] of longint;
    viz:array[0..1000000] of 0..1;
    f,g:text;
    i,n,j,k,u,m,i_s,x,y,sol:longint;
procedure df(nod:longint);
begin
    viz[k]:=1;
    for k:=1 to n do
        if (viz[k]=0) and (a[nod,k]=1) then df(k);
end;
begin
assign(f,'dfs.in');reset(F);
assign(g,'dfs.out');rewrite(G);
readln(f,n,m);
for i:=1 to m do begin
         readln(f,x,y);
         a[x,y]:=1;
         a[y,x]:=1;
                end;
viz[1]:=1;
for i:=1 to n do
        if  viz[i]=0 then begin
                        inc(sol);
                        df(i);
                          end;
writeln(G,sol);
close(F);
close(G);
end.