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

#include <bits/stdc++.h>
using namespace std;



int main() {
	string k;
	cin>>k;
	for(int i=0;i<k.length();i++){
		if(k[i]=='A') k[i]='T';
		else if(k[i]=='T') k[i]='A';
		else if(k[i]=='G') k[i]='C';
		else if(k[i]=='C') k[i]='G';
	}
	cout<<k;
    return 0;
}

```依旧字符串数组/.