import java.util.*;
import java.io.*;

public class Main {

    private static FastScanner sc = new FastScanner();

    public static void main(String[] args) {


        String s = sc.nextLine();

        char[] acgt = {'A','G','T','C'};

        int max = 0;
        int count = 0;
        for(int i = 0; i < s.length();i++){
            for(int j = 0;j<4;j++){
                if(acgt[j] == s.charAt(i)){
                    count++;
                    if(max < count){
                        max = count;
                    }
                    break;
                }
                if(j == 3){
                    count = 0;
                }
            }
        }

        System.out.println(max);

    }
}

class FastScanner extends PrintWriter {
    private final InputStream in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    FastScanner() {
        this(System.in);
    }

    FastScanner(InputStream source) {
        super(System.out);
        this.in = source;
    }

    boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    int readByte() {
        if (hasNextByte()) return buffer[ptr++];
        else return -1;
    }

    boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    boolean isNewLine(int c) {
        return c == '\n' || c == '\r';
    }

    void skipUnprintable() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
    }

    void skipNewLine() {
        while (hasNextByte() && isNewLine(buffer[ptr])) ptr++;
    }

    boolean hasNext() {
        skipUnprintable();
        return hasNextByte();
    }

    boolean hasNextLine() {
        skipNewLine();
        return hasNextByte();
    }

    String next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    char[] nextCharArray(int len) {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        char[] s = new char[len];
        int i = 0;
        int b = readByte();
        while (isPrintableChar(b)) {
            if (i == len) {
                throw new InputMismatchException();
            }
            s[i++] = (char) b;
            b = readByte();
        }
        return s;
    }

    String nextLine() {
        if (!hasNextLine()) {
            throw new NoSuchElementException();
        }
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (!isNewLine(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    long nextLong() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
            throw new NumberFormatException();
        }
        return (int) nl;
    }

    char nextChar() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        return (char) readByte();
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    int[] arrayInt(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    }

    long[] arrayLong(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    }

    double[] arrayDouble(int n) {
        double[] a = new double[n];
        for (int i = 0; i < n; i++) a[i] = nextDouble();
        return a;
    }

    void arrayInt(int[]... a) {
        for (int i = 0; i < a[0].length; i++) for (int j = 0; j < a.length; j++) a[j][i] = nextInt();
    }

    int[][] matrixInt(int n, int m) {
        int[][] a = new int[n][];
        for (int i = 0; i < n; i++) a[i] = arrayInt(m);
        return a;
    }

    char[][] mapChar(int n, int m) {
        char[][] a = new char[n][];
        for (int i = 0; i < n; i++) a[i] = nextCharArray(m);
        return a;
    }

    public void close() {
        super.close();
        try {
            in.close();
        } catch (IOException ignored) {
        }
    }
}


Measured memory_bytes: 22996