只要判断一项

#include<bits/stdc++.h>//submitRecord//
using namespace std;
//const int N=1e7+10;
int main(){
//freopen("","r",stdin);
//freopen("","w",stdout);
ios::sync_with_stdio();
cin.tie(nullptr);
cout.tie(nullptr);
int n;
cin>>n;
if(n>=90) cout<<"A";
else if(n>79) cout<<"B";
else if(n>69) cout<<"C";
else if(n>59) cout<<"D";
else cout<<"E";
//fclose(stdin);
//fclose(stdout);
return 0;
}