习题：找回密码（高精度逆向模拟）

program find;
var
  a,b,c:array[0..2000001]of longint;
  r:array[0..9]of longint=(0,7,4,1,8,5,2,9,6,3);
  e:array[0..9]of longint=(0,2,1,0,2,1,0,2,1,0);
  n,i,m:longint;
  s:ansistring;
procedure get;
var i,s,v,x,k:longint;
begin
  s:=0; v:=0;
  for i:=n downto 1 do
   begin
    if b[i]<0 then k:=(abs(b[i]) div 10+ord(abs(b[i]) mod 10<>0)) else k:=0;
    if b[i]<0 then b[i]:=k*10-abs(b[i]);
    c[i]:=r[b[i]];  b[i-1]:=b[i-1]-e[b[i]]-k;
   end;
  for i:=1 to n do
   write(c[i]);
end;
procedure work;
var i,s,v,x,k:longint;
begin
  s:=0; v:=0;
  for i:=n downto 1 do
   begin
     if i=1 then v:=v-b[n]+(r[a[n]]*2)mod 10;
     if v<=a[i] then k:=0
      else k:=(v-a[i]) div 10+ord((v-a[i]) mod 10>0);
     x:=a[i]+k*10-v;
     b[i]:=x;
     a[i-1]:=a[i-1]-k;
     v:=v+x;
   end;
  get;
end;
begin
  readln(s);
  n:=length(s);
  for i:=1 to n do
   a[i]:=ord(s[i])-48;
  work;
end.