uses crt;
var a,b,c,d:integer;
begin
clrscr;
write('So hoc sinh lop 6= ');readln(a);
write('So hoc sinh lop 7= ');readln(b);
write('So hoc sinh lop 8= ');readln(c);
write('So hoc sinh lop 9= ');readln(d);
writeln('Tong so hoc sinh cua truong la: ',a+b+c+d);
readln;
end.