#include <bits/stdc++.h>
#include <string>

/**Define file I/O **/
#define f_input freopen("input.txt","r",stdin)
#define f_output freopen("output.txt","w",stdout)

/**Define memory set function**/
#define mem(x,y) memset(x,y,sizeof(x))
#define CLEAR(x) memset(x,0,sizeof(x))

/**Define function and object**/
#define pb push_back
#define Sort(v) sort(v.begin(),v.end())
#define RSort(v) sort(v.rbegin(),v.rend())
#define CSort(v,C) sort(v.begin(),v.end(),C)
#define all(v) (v).begin(),(v).end()
#define sqr(x) ((x)*(x))
#define find_dist(a,b) sqrt(sqr(a.x-b.x)+sqr(a.y-b.y))

/**Define constant value**/
#define ERR 1e-9
#define pi (2*acos(0))
#define PI 3.141592653589793

/**Define input**/
#define scanint(a) scanf("%d",&a)
#define scanLLD(a) scanf("%lld",&a)
#define scanstr(s) scanf("%s",s)
#define scanline(l) scanf(" %[^\n]",l);

/**Define Bitwise operation**/
#define check(n, pos) (n & (1<<(pos)))
#define biton(n, pos) (n | (1<<(pos)))
#define bitoff(n, pos) (n & ~(1<<(pos)))

/**Define color**/
enum {WHITE,GREY,BLACK};

/**Sync off with stdio**/
#define __ cin.sync_with_stdio(false);\
           cin.tie();
/**Debug tools**/
#define what_is(x) cerr<<(#x)<<" is "<<x<<endl
using namespace std;

/**Typedef**/
typedef vector<int> vint;
typedef vector< vint > vint2D;
typedef vector<string> vstr;
typedef vector<char>vchar;
typedef vector< vchar >vchar2D;
typedef queue<int> Qi;
typedef queue< Qi > Qii;
typedef map<int,int> Mii;
typedef map<string,int> Msi;
typedef map<int,string> Mis;
typedef stack<int> stk;
typedef pair<int,int> pp;
typedef pair<int, pp > ppp;
typedef long long int LLD;
const int inf=0x7FFFFFFF;

/**Template & structure**/
struct point_int{int x,y;point_int(){}point_int(int a,int b){x=a,y=b;}
    bool operator==(const point_int &a)const{return x==a.x and y==a.y;}
}; ///Point for x,y (int) coordinate in 2D space
struct point_double{double x,y;point_double(){}point_double(double a,double b){x=a,y=b;}}; ///Point for x,y (double) coordinate in 2D space
struct Node{int v,w;Node() {}bool operator<(const Node &a)const{return w>a.w;}Node(int _v,int _w){v=_v,w=_w;}};///Node for Dijkstra
namespace my{
template<class T>T gcd(T a,T b){return b == 0 ? a : gcd(b, a % b);}

template<typename T>T lcm(T a, T b) {return a / gcd(a,b) * b;}

template<class T>T big_mod(T n,T p,T m){if(p==0)return (T)1;T x=big_mod(n,p/2,m);x=(x*x)%m;if(p&1)x=(x*n)%m;return x;}

template<class T>T multiplication(T n,T p,T m){if(p==0)return (T)0;T x=multiplication(n,p/2,m);x=(x+x)%m;if(p&1)x=(x+n)%m;return x;}

template<class T>T my_pow(T n,T p){if(p==0)return 1;T x=my_pow(n,p/2);x=(x*x);if(p&1)x=(x*n);return x;} ///n to the power p

template <class T> double getdist(T a, T b){return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));}// distance between a & b

template <class T> T extract(string s, T ret) {stringstream ss(s); ss >> ret; return ret;}// extract words or numbers from a line

template <class T> string tostring(T n) {stringstream ss; ss << n; return ss.str();}// convert a number to string

template<class T> inline T Mod(T n,T m) {return (n%m+m)%m;} ///For Positive Negative No.

template<class T> T MIN3(T a,T b,T c) {return min(a,min(b,c));} // minimum of 3 number

template<class T> T MAX3(T a,T b,T c) {return max(a,max(b,c));} ///maximum of 3 number

template <class T> void print_vector(T &v){int sz=v.size();if(sz)cout<<v[0];for(int i = 1; i < sz; i++)cout << ' '<<v[i];cout<<"\n";}// prints all elements in a vector

bool isVowel(char ch){ ch=toupper(ch); if(ch=='A'||ch=='U'||ch=='I'||ch=='O'||ch=='E') return true; return false;}

bool isConsonant(char ch){if (isalpha(ch) && !isVowel(ch)) return true; return false;}}

namespace debug{
    int sum(){return 0;}
    template<typename T,typename... Args> T sum(T a,Args... args) {return a+sum(args...);}
    void print(){cout<<"\n";return;}template<typename T, typename... Args>void print(T a,Args... args){cout<<a<<" ";print(args...);}
}

/**Shortcut input function**/
int read_int(){int n;scanf("%d",&n);return n;}

int read_LLD(){LLD n;scanf("%lld",&n);return n;}

inline int buffer_input() { char inp[1000]; scanstr(inp); return atoi(inp); }

/**Direction**/
///int dx[8] = {0, 1, 1, 1, 0, -1, -1, -1};int dy[8] = {1, 1, 0, -1, -1, -1, 0, 1}; ///8 Direction
///int dx[4] = {1, 0, -1, 0};int dy[4] = {0, 1, 0, -1}; ///4 Direction
///int dx[]={2,1,-1,-2,-2,-1,1,2};int dy[]={1,2,2,1,-1,-2,-2,-1};///Knight Direction
///int dx[]={-1,-1,+0,+1,+1,+0};int dy[]={-1,+1,+2,+1,-1,-2}; ///Hexagonal Direction


/******************************End******************************/
void solve()
{
    string n;
    cin >> n;
    if(n=="C")cout << "G" << endl;
    else if(n=="G")cout << "C" << endl;
    else if(n=="A")cout << "T" << endl;
    else if(n=="T") cout << "A" << endl;
}
int main()
{
    solve();
    return 0;
}



Measured memory_bytes: 256