#include<stdio.h>
main()
{
	char fin[100], fout[100];
	for(int i = 1 ; i <= 5 ; i++ )
	{
		sprintf(fin,".%d.in",i);
		sprintf(fout,".%d.out",i);
		freopen(fin,"r",stdin);
		freopen(fout,"w",stdout);
		int a, b, c;
		scanf("%d",&a);
		switch(a/10)
		{
		    case 10 : case 9 :puts("A");break;
		    case 8 :  case 7 : puts("B"); break;
		    case 6 : case 5: case 4: puts("C"); break;
		    default : puts("D");
		}

	}
}