import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.BufferedWriter;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.IOException;
import java.util.InputMismatchException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author lewin
 */
public class ketek_counting_lewin {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        ketekcounting solver = new ketekcounting();
        solver.solve(1, in, out);
        out.close();
    }

    static class ketekcounting {
        int mod = 998244353;
        int c1;
        int c2;
        char[] c;
        long[] dp;

        public int getMult(char a, char b) {
            if (a == '?' && b == '?') return 26;
            if (a == '?' || b == '?') return 1;
            return (a == b) ? 1 : 0;
        }

        public void solve(int testNumber, InputReader in, OutputWriter out) {
            String s = in.next();
            int mult = 1;
            if (s.length() % 2 == 1) {
                if (s.charAt(s.length() / 2) == '?') mult = 26;
                s = s.substring(0, s.length() / 2) + s.substring(s.length() / 2 + 1);
            }
            c = s.toCharArray();
            int t = c.length / 2;
            c1 = c.length / 2 - 1;
            c2 = c1 + 1;
            dp = new long[t + 1];
            dp[0] = 1;
            long cf = 1;
            for (int i = 0; i < t; i++) {
                cf = cf * getMult(c[c1 - i], '?') * getMult(c[c2 + i], '?') % mod;
                dp[i + 1] = cf;
            }
            for (int i = 0; i < t; i++) {
                expand(c1 - i, c1 - i, c2 + i, c2 + i);
                expand(c1 - i - 1, c1 - i, c2 + i, c2 + i + 1);
            }


            out.println(dp[t] * mult % mod);
        }

        boolean in_range(int x) {
            return 0 <= x && x < c.length;
        }

        void expand(int a1, int a2, int b1, int b2) {
            if (!in_range(a1) || !in_range(a2) || !in_range(b1) || !in_range(b2)) return;
            long cf = getMult(c[a1], c[b1]);
            if (a2 != a1) cf = cf * getMult(c[a2], c[b2]) % mod;
            do {
                dp[b2 - c2 + 1] = (dp[b2 - c2 + 1] + dp[b1 - c2] * cf) % mod;
            } while (in_range(--a1) && in_range(++a2) && in_range(--b1) && in_range(++b2) &&
                    a2 < b1 &&
                    (cf = cf * getMult(c[a1], c[b1]) * getMult(c[a2], c[b2]) % mod) > 0);
        }

    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void close() {
            writer.close();
        }

        public void println(long i) {
            writer.println(i);
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1 << 16];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (this.numChars == -1) {
                throw new UnknownError();
            } else {
                if (this.curChar >= this.numChars) {
                    this.curChar = 0;

                    try {
                        this.numChars = this.stream.read(this.buf);
                    } catch (IOException var2) {
                        throw new InputMismatchException();
                    }

                    if (this.numChars <= 0) {
                        return -1;
                    }
                }

                return this.buf[this.curChar++];
            }
        }

        public String next() {
            int c;
            while (isSpaceChar(c = this.read())) {
                ;
            }

            StringBuilder result = new StringBuilder();
            result.appendCodePoint(c);

            while (!isSpaceChar(c = this.read())) {
                result.appendCodePoint(c);
            }

            return result.toString();
        }

        public static boolean isSpaceChar(int c) {
            return c == 32 || c == 10 || c == 13 || c == 9 || c == -1;
        }

    }
}