import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Arrays;

public class Main {
public static void main(String[] args) {
	InputStream inputStream = System.in;
	OutputStream outputStream = System.out;
	MyInput in = new MyInput(inputStream);
	PrintWriter out = new PrintWriter(outputStream);
	TaskX solver = new TaskX();
	solver.solve(1, in, out);
	out.close();
}

static int INF = 1 << 30;
static long LINF = 1L << 55;
static int MOD = 1000000007;
static int[] mh4 = { 0, -1, 1, 0 };
static int[] mw4 = { -1, 0, 0, 1 };
static int[] mh8 = { -1, -1, -1, 0, 0, 1, 1, 1 };
static int[] mw8 = { -1, 0, 1, -1, 1, -1, 0, 1 };

static class TaskX {

	public void solve(int testNumber, MyInput in, PrintWriter out) {

		char[] s = in.nextChars();
		int n = s.length;
		int ans = 0;
		for (int i = 0; i < n; i++) {
			for (int j = i; j < n; j++) {
				boolean ok = true;
				for (int k = i; k <= j; k++) {
					if (!(s[k] == 'A' || s[k] == 'G' || s[k] == 'C' || s[k] == 'T')) {
						ok = false;
					}
				}
				if (ok) {
					ans = Math.max(ans, j-i+1);
				}
			}
		}

		out.println(ans);

	}
}

static class MyInput {
	private final BufferedReader in;
	private static int pos;
	private static int readLen;
	private static final char[] buffer = new char[1024 * 8];
	private static char[] str = new char[500 * 8 * 2];
	private static boolean[] isDigit = new boolean[256];
	private static boolean[] isSpace = new boolean[256];
	private static boolean[] isLineSep = new boolean[256];

	static {
		for (int i = 0; i < 10; i++) {
			isDigit['0' + i] = true;
		}
		isDigit['-'] = true;
		isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
		isLineSep['\r'] = isLineSep['\n'] = true;
	}

	public MyInput(InputStream is) {
		in = new BufferedReader(new InputStreamReader(is));
	}

	public int read() {
		if (pos >= readLen) {
			pos = 0;
			try {
				readLen = in.read(buffer);
			} catch (IOException e) {
				throw new RuntimeException();
			}
			if (readLen <= 0) {
				throw new MyInput.EndOfFileRuntimeException();
			}
		}
		return buffer[pos++];
	}

	public int nextInt() {
		int len = 0;
		str[len++] = nextChar();
		len = reads(len, isSpace);
		int i = 0;
		int ret = 0;
		if (str[0] == '-') {
			i = 1;
		}
		for (; i < len; i++)
			ret = ret * 10 + str[i] - '0';
		if (str[0] == '-') {
			ret = -ret;
		}
		return ret;
	}

	public long nextLong() {
		int len = 0;
		str[len++] = nextChar();
		len = reads(len, isSpace);
		int i = 0;
		long ret = 0;
		if (str[0] == '-') {
			i = 1;
		}
		for (; i < len; i++)
			ret = ret * 10 + str[i] - '0';
		if (str[0] == '-') {
			ret = -ret;
		}
		return ret;
	}

	public char nextChar() {
		while (true) {
			final int c = read();
			if (!isSpace[c]) {
				return (char) c;
			}
		}
	}

	public String nextString() {
		return new String(nextChars());
	}

	public char[] nextChars() {
		int len = 0;
		str[len++] = nextChar();
		len = reads(len, isSpace);
		return Arrays.copyOf(str, len);
	}

	public char[][] next2DChars(int h, int w) {
		char[][] s = new char[h][w];
		for (int i = 0; i < h; i++) {
			s[i] = nextChars();
		}
		return s;
	}

	int reads(int len, boolean[] accept) {
		try {
			while (true) {
				final int c = read();
				if (accept[c]) {
					break;
				}
				if (str.length == len) {
					char[] rep = new char[str.length * 3 / 2];
					System.arraycopy(str, 0, rep, 0, str.length);
					str = rep;
				}
				str[len++] = (char) c;
			}
		} catch (MyInput.EndOfFileRuntimeException e) {
		}
		return len;
	}

	public int[] nextIntArray(final int n) {
		final int[] res = new int[n];
		for (int i = 0; i < n; i++) {
			res[i] = nextInt();
		}
		return res;
	}

	public int[] nextIntArray1Index(final int n) {
		final int[] res = new int[n + 1];
		for (int i = 1; i < n + 1; i++) {
			res[i] = nextInt();
		}
		return res;
	}

	public int[] nextIntArrayDec(final int n) {
		final int[] res = new int[n];
		for (int i = 0; i < n; i++) {
			res[i] = nextInt() - 1;
		}
		return res;
	}

	public long[] nextLongArray(final int n) {
		final long[] res = new long[n];
		for (int i = 0; i < n; i++) {
			res[i] = nextLong();
		}
		return res;
	}

	public long[] nextLongArray1Index(final int n) {
		final long[] res = new long[n + 1];
		for (int i = 1; i < n + 1; i++) {
			res[i] = nextLong();
		}
		return res;
	}

	public long[] nextLongArrayDec(final int n) {
		final long[] res = new long[n];
		for (int i = 0; i < n; i++) {
			res[i] = nextLong() - 1;
		}
		return res;
	}

	public double nextDouble() {
		return Double.parseDouble(nextString());
	}

	public double[] nextDoubleArray(int n) {
		double[] res = new double[n];
		for (int i = 0; i < n; i++) {
			res[i] = nextDouble();
		}
		return res;
	}

	static class EndOfFileRuntimeException extends RuntimeException {
	}

}
}


Measured memory_bytes: 21588