import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) B solver = new B(); solver new B() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

    } B public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        } solve {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        } String S = in.next(); S in.next() in.next in int cnt = 0; cnt 0 int ans = 0; ans 0 for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            } {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            } cnt = 0 cnt 0 for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                } int j = i; int j = i; j i j < S.length() j S.length() S.length S j++ j++ j {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                } {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                } if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    } 'A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j) 'G' == S.charAt(j) 'A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j) 'A' == S.charAt(j) 'A' S.charAt(j) S.charAt S j 'C' == S.charAt(j) 'C' S.charAt(j) S.charAt S j 'G' == S.charAt(j) 'G' S.charAt(j) S.charAt S j 'T' == S.charAt(j) 'T' S.charAt(j) S.charAt S j {
                        cnt++;
                    } cnt++ cnt {
                        break;
                    } break; ans = Math.max(ans, cnt) ans Math.max(ans, cnt) Math.max Math ans cnt out.println(ans) out.println out ans int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

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

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        B solver = new B();
        solver.solve(1, in, out);
        out.close();
    }

    static class B {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            String S = in.next();

            int cnt = 0;
            int ans = 0;
            for (int i = 0; i < S.length(); i++) {
                cnt = 0;
                for (int j = i; j < S.length(); j++) {
                    if ('A' == S.charAt(j) || 'C' == S.charAt(j) || 'G' == S.charAt(j) || 'T' == S.charAt(j)) {
                        cnt++;
                    } else {
                        break;
                    }
                    ans = Math.max(ans, cnt);
                }
            }
            out.println(ans);
        }

    }
}

