Tim vi tri 1000 la so bao nhieu cua day

Tim vi tri 1000 la so bao nhieu cua day
Const
fi='num.inp';
fo='num.out';
Var
cs:array[1..7] of longint = (9,180,2700,36000,450000,5400000,63000000);
n:longint;
f,g:text;
Function num(n:longint):char;
Var
k,so,mu:longint;
s:string;
Begin
k:=1;
mu:=1;
While (k<9) and (cs[k]Begin
n:=n-cs[k];
inc(k);
mu:=mu*10;
End;
If mu=1 then
so:=n div k
Else
so:=n div k+mu+ord(n mod k>0)-1;
Str(so,s);
s:=s[k]+s;
num:=s[n mod k + 1];
End;
Begin
Assign(f,fi);

Reset(f);
Assign(g,fo);
Rewrite(g);
While not seekeof(f) do
Begin
Readln(f,n);
Writeln(g,num(n));
End;
Close(f);
Close(g);
End.


var st: string;
j,n,d,x: longint;
i: integer;
f:text;
begin
clrscr;
write('Nhap n: ');readln(n);
i:=1;
j:=1;
d:=9;
x:=0;
while (n > d) do
begin
n:=n-d;
x:=x+d div i;
j:=j*10;
i:=i+1;

d:=j*9*i;
end;
x:=x+(n div i);
if n mod i>0 then
begin
x:=x+1;
i:=n mod i;
end;
str(x,st);
write('Ket qua: ',st[i]);
end.