题解在此

#include <iostream>
using namespace std;
int main(){
    string s;
    cin>>s;
    for (int i=0;i<s.size();i++){
        if (s[i]=='a'||s[i]=='c'||s[i]=='g'||s[i]=='o'){
            s[i]-=32;
        }else if (s[i]>='A'&&s[i]<='Z'&&s[i]!='A'&&s[i]!='C'&&s[i]!='G'&&s[i]!='O'){
            s[i]+=32;
        }
    }
    cout<<s;
    return 0;
}