#include<iostream> #include<cstdio> //scanf()\printf() using namespace std; int main(){ int n; cin>>n; if(n>=0&&n<=100) switch(n/10){ case 10: case 9:printf("A");break; case 8: case 7:printf("B");break; case 6:printf("C");break; case 5: case 4: case 3: case 2: case 1: case 0:printf("D");break; } return 0; }