太简单了哈哈哈哈

#include<iostream>
using namespace std;
int main(){
int a;
cin >> a;
if (a >=90 and a<100) cout<<"A";
else if (a >=80 and a<90) cout<<"B";
else if (a >=70 and a<80) cout<<"C";
else if (a >=60 and a<70) cout<<"D";
else cout<<"E";

return 0;

}