program diningb;
var
n,i:longint;
a:array[1..30000] of longint;
f:array[0..30000,1..2] of longint;
function min(a,b:longint):longint;
begin
if a>b then min:=b
else min:=a;
end;
begin
assign(input,'diningb.in');
reset(input);
assign(output,'diningb.out');
rewrite(output);
while not eof do begin
read(n);
for i:=1 to n do read(a[i]);
f[0,1]:=0;
f[0,2]:=0;
for i:=1 to n do
if a[i]=1 then
  begin
  f[i,1]:=f[i-1,1];
  f[i,2]:=min(f[i-1,1],f[i-1,2]+1);
  end
  else
  begin
  f[i,1]:=f[i-1,1]+1;
  f[i,2]:=min(f[i-1,1]+1,f[i-1,2]);
  end;
if f[n,1]>f[n,2] then
writeln(f[n,2])
else writeln(f[n,1]);
end;
close(input);
close(output);
end.