#include <iostream>

using namespace std;

int N, x[200001][4], M;
string s;

int main()
{
	cin >> s;
	N = s.length();

	int A = 0, G = 0, C = 0, T = 0, sA = 0, sG = 0, sC = 0, sT = 0, hA = 0, hC = 0, hG = 0, hT = 0;

	for (int i = 0; i < N; ++i) {
		if (s[i] == 'A') {
			if (sA == 0) sA = i;
			hA = i - sA;
			++A;
		}
		else if (s[i] == 'C') {
			if (sC == 0) sC = i;
			hC = i - sC;
			++C;
		}
		else if (s[i] == 'G') {
			if (sG == 0) sG = i;
			hG = i - sG;
			++G;
		}
		else {
			if (sT == 0) sT = i;
			hT = i - sT;
			++T;
		}
	}

	if (2 * A >= hA) M = max(2 * A, M);
	if (2 * C >= hC) M = max(2 * C, M);
	if (2 * G >= hG) M = max(2 * G, M);
	if (2 * T >= hT) M = max(2 * T, M);

	cout << M << '\n';
	return 0;
}