#include
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n==1)
	       cout<<"A";
	if(n==2)
	       cout<<"B";
	if(n==3)
	       cout<<"C";	          
	if(n==4)
	       cout<<"D";       
    return 0;
}

满分题解：

#include<bits/stdc++.h> 
using namespace std; 
int main(){ 
  int a,b; 
  cin>>a>>b; 
  if(abs(a%2)==1 and abs(b%2)==1) 
  cout<<2; 
  else if(abs(a%2)==1 or abs(b%2)==1) 
  cout<<1; 
  else cout<<0; 
  return 0; }

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n==1) 
		cout<<"A";
	if(n==2) 
		cout<<"B";
	if(n==3) 
		cout<<"C";
	if(n==4) 
		cout<<"D";
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n==1) 
		cout<<"A";
	if(n==2) 
		cout<<"B";
	if(n==3) 
		cout<<"C";
	if(n==4) 
		cout<<"D";
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n==1) 
		cout<<"A";
	if(n==2) 
		cout<<"B";
	if(n==3) 
		cout<<"C";
	if(n==4) 
		cout<<"D";
	return 0;
}