111111
 100009
 10011
 1000000
 8
 10201
 102030
 908172
 123456
 415
 900000
 21
 909090
 314159
 999999
 909823
 987654
 1453
 1435
 98
 10
 2
 1

1
111111
 9
100001 1 1 1 1 1 1 1 1
 1
10011
 1
1000000
 8
1 1 1 1 1 1 1 1
 2
10101 100
 3
101010 1010 10
 9
101111 101011 101010 101010 101010 101010 101010 101000 100000
 6
111111 11111 1111 111 11 1
 5
111 101 101 101 1
 9
100000 100000 100000 100000 100000 100000 100000 100000 100000
 2
11 10
 9
101010 101010 101010 101010 101010 101010 101010 101010 101010
 9
111111 101011 101011 1011 11 1 1 1 1
 9
111111 111111 111111 111111 111111 111111 111111 111111 111111
 9
101111 101111 101101 101100 101100 101100 101100 101100 101000
 9
111111 111111 111111 111111 111110 111100 111000 110000 100000
 5
1111 111 111 110 10
 5
1111 111 111 101 1
 9
11 11 11 11 11 11 11 11 10
 1
10
 2
1 1
 1
1

import org.omg.CORBA.CODESET_INCOMPATIBLE;

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

public class Main {
    private static StringTokenizer st;
    private static BufferedReader br;
    public static long MOD = 1000000007;
    private static double EPS = 0.000001;

    public static void print(Object x) {
        System.out.println(x + "");
    }
    public static void printArr(long[] x) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < x.length; i++) {
            s.append(x[i] + " ");
        }
        print(s);
    }
    public static void printArr(int[] x) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < x.length; i++) {
            s.append(x[i] + " ");
        }
        print(s);
    }
    public static void printArr(char[] x) {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < x.length; i++) {
            s.append(x[i] + "");
        }
        print(s);
    }
    public static String join(Collection<?> x, String space) {
        if (x.size() == 0) return "";
        StringBuilder sb = new StringBuilder();
        boolean first = true;
        for (Object elt : x) {
            if (first) first = false;
            else sb.append(space);
            sb.append(elt);
        }
        return sb.toString();
    }

    public static String nextToken() throws IOException {
        while (st == null || !st.hasMoreTokens()) {
            String line = br.readLine();
            st = new StringTokenizer(line.trim());
        }
        return st.nextToken();
    }
    public static int nextInt() throws IOException {
        return Integer.parseInt(nextToken());
    }
    public static long nextLong() throws IOException {
        return Long.parseLong(nextToken());
    }
    public static List<Integer> nextInts(int N) throws IOException {
        List<Integer> ret = new ArrayList<Integer>();
        for (int i = 0; i < N; i++) {
            ret.add(nextInt());
        }
        return ret;
    }

    public static void main(String[] args) throws IOException {
        br = new BufferedReader(new InputStreamReader(System.in));

        int n = nextInt();
        int max = 0;
        while (n > 0) {
            max = Math.max(max, n % 10);
            n /= 10;
        }
        print(max);
    }
}
