Conversion 2-10

uses wincrt;
var
ch:string;


function test(ch:string):boolean;
var
i:integer;
begin
i:=1;
while (ch[i] in ['0'..'1']) and (i<length(ch)) do
i:=i+1;
if(not(ch[i] in ['0'..'1'])) then test:=false
else test:=true;
end;
procedure saisir_ch(var ch:string);
begin
repeat
write('ch=');
readln(ch);
until(test(ch));
end;

function puissance(x,y:integer):longint;
var
i,p:longint;
begin
p:=1;
for i:=1 to y do
p:=p*x;
puissance:=p;
end;
function conv210(ch:string):integer;
var
i,d,e,s:integer;
begin
s:=0;
for i:=length(ch) downto 1 do
begin
val(ch[i],d,e);
s:=s+(d*puissance(2,length(ch)-i));
end;
conv210:=s;
end;
begin
saisir_ch(ch);
writeln(conv210(ch));
end.