program btod;
var
  b:string;
  str1:char;
  d,i,y,l:integer;
  a:array [1..20] of integer;
begin
  write('Input the Binary Number:');readln(b);
  l:=length(b);
  for i:=1 to l do
    begin
      str1:=b[i];
      a[i]:=ord(str1)-48;
    end;

  y:=1;d:=a[l];
  for i:=l-1 downto 1 do
    begin
      y:=y*2;
      d:=d+a[i]*y;
    end;
  writeln(d);
end.