C :

#include <stdio.h>
void main()
{
	int x;
	scanf("%d",&x);
	switch(x/10)
	{
		case 0:printf("A\n");break;
		case 1:printf("B\n");break;
		case 2:case 3:printf("C\n");break;
		case 4:printf("D\n");break;
		default:printf("E\n");
	}
}

Pascal :

var x:integer;
begin
  readln(x);
  case x of
    0..9:writeln('A');
	10..19:writeln('B');
	20..39:writeln('C');
	40..49:writeln('D');
	50..79:writeln('E');
  end;
end.