题解

#include<iostream>
using namespace std;
int main(){
    string a;
    cin>>a;
    for(int i=0;i<a.size();i++){
        if(a[i]=='A'){cout<<"T";
}else if(a[i]=='T'){cout<<"A";
}else if(a[i]=='G'){cout<<"C";
}else if(a[i]=='C'){cout<<"G";
}
        }
    return 0;
}