A403.配对碱基链

#include<iostream>
using namespace std;
int main(){
    char ch;
    while(cin>>ch){
        if(ch=='A') cout<<'T';
        else if(ch=='T') cout<<'A';
        else if(ch=='G') cout<<'C';
        else if(ch=='C') cout<<'G';
    }
    return 0;
}