#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int a; cin>>a; a=a/10; switch(a){ case 10: case 9: cout<<'A'<<endl;break; case 8: case 7: cout<<'B'<<endl;break; case 6: cout<<'C'<<endl;break; default:cout<<'D';break; } return 0; }