uses crt;
var ly,toan,van:real;
begin
clrscr;
repeat
write('Diem Toan='); readln(toan);
write('Diem Van='); readln(van);
write('Diem Ly='); readln(ly);
until (toan>0) and (van>0) and (ly>0);
writeln('Diem trung binh cua 3 mon la: ',(toan+van+ly)/3:4:2);
readln;
end.