program panel;
var f,g:text;
    n,p,c,i:integer;
    v:array[1..100] of 0..1;
begin
 assign(f,'panel.in');
 reset(f);
 assign(g,'panel.out');
 rewrite(g);
 readln(f,n);
 for i:=1 to n do
   read(f,v[i]);
 c:=0;
 for i:=1 to n-1 do
   if (v[i]=1) and (v[i+1]=1) then
     begin
       v[i+1]:=0;
       c:=c+1;
     end
   else
   if (v[i]=0) and (v[i+1]=0) then
     begin
       v[i+1]:=1;
       c:=c+1;
     end;
 writeln(g,c);
 close(f);
 close(G);
end.