program nou;
 var a:array[0..10000,0..10000] of longint;
     x,y,i,j:longint;
     n,m,c,cc,ccc,ccd:qword;
     f,g:Text;
      procedure citire;
       var i,j,l:integer;
        begin
         assign(f,'dfs.in');
         reset(f);
         assign(g,'dfs.out');
         rewrite(g);
         readln(f,n,m);
            for j:=1 to m do
            begin
             read(f,x,y);
             a[x,y]:=1;
             a[y,x]:=1;
            end;
           end;
         begin
          citire;
          c:=0;
          cc:=0;
          ccc:=0;
           for i:=1 to n do
            begin
            if i<n-1 then
            ccc:=0;
             for j:=1 to n do
               if a[i,j]=1 then
                begin
                 ccc:=ccc+1;
                end;
             end;
             if ccc=0 then
              begin
                   for i:=1 to n-1 do
                begin
                c:=0;
                 for j:=i+1 to n do
                 begin
                  if a[i,j]=1 then
                   c:=c+1;
                 end;
                  if c=0 then
                   cc:=cc+1;
                end;
                for i:=n to n do
                 begin
                  for j:=1 to n do
                   if a[i,j]=1 then
                    ccd:=ccd+1;
                 end;
                  if ccd=0 then
                   write(g,cc)
                   else
                   write(g,cc+1);
               end
                else
                 begin
                 for i:=1 to n-1 do
                begin
                c:=0;
                 for j:=i+1 to n do
                 begin
                  if a[i,j]=1 then
                   c:=c+1;
                 end;
                  if c=0 then
                   cc:=cc+1;
                end;
                 write(g,cc);
                 end;
         close(f);
         close(g);
        end.