program bai7;
uses crt;
var tcha,tcon,nam:integer;
begin
clrscr;
write('nhap vao tuoi cha va tuoi con '); readln(tcha,tcon);
nam:=0;
while(tcha<>tcon*2) do
begin
tcha:=tcha+1;
tcon:=tcon+1;
nam:=nam+1;
end;
writeln('sau ',nam,' nam nua thi tuoi cha gap 2 lan tuoi con');
readln;
end.