DANHBAI PASCAL

var     a,b,d:array [0..1000000] of longint;
    n,x,y:longint;
procedure nhap;
var i,u:longint;
begin
    readln(n);
    for i:=1 to n do
    begin
        readln(u);
        inc(d[u]);
    end;
end;

procedure tao_mang;
var i:longint;
begin
    for i:=1 to 2*n do
        if d[i]=1 then
        begin
            inc(x);a[x]:=i;
        end
        else
        begin
            inc(y);b[y]:=i;
        end;
end;

procedure giai;
var i,j,t:longint;
begin
    i:=1; t:=0;
    for j:=1 to n do
        if b[j]>a[i] then
        begin
            inc(i);inc(t);
        end;
    write(t);
end;

begin
    assign(input,'danhbai.inp');reset(input);
    assign(output,'danhbai.out');rewrite(output);
    nhap;
    tao_mang;
    giai;
end.