Problem:
Score: 600 points

Problem Statement

How many strings can be obtained by applying the following operation on a string S exactly K times: "choose one lowercase English letter and insert it somewhere"?

The answer can be enormous, so print it modulo (10^9+7).

Constraints

K is an integer between 1 and 10^6 (inclusive).

S is a string of length between 1 and 10^6 (inclusive) consisting of lowercase English letters.

Input

Input is given from Standard Input in the following format:

K
S

Output

Print the number of strings satisfying the condition, modulo (10^9+7).

Sample Input 1

5
oof

Sample Output 1

575111451

For example, we can obtain proofend, moonwolf, and onionpuf, while we cannot obtain oofsix, oofelevennn, voxafolt, or fooooooo.

Sample Input 2

37564
whydidyoudesertme

Sample Output 2

318008117

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

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

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

    static class FStrivore {
        long modExp(long x, long y, long mod) {
            if (y == 0)
                return 1 % mod;
            long ret = modExp(x, y >> 1, mod);
            ret = ret * ret % mod;
            if ((y & 1) == 1)
                ret = ret * (x % mod) % mod;
            return ret;
        }

        public void solve(int testNumber, InputReader s, PrintWriter w) {
            long mod = (long) 1e9 + 7;
            int k = s.nextInt();
            char[] a = s.next().toCharArray();
            int n = a.length;
            long res = 0;
            long[] pow25 = new long[k + n + 1];
            pow25[0] = 1;
            long[] pow26 = new long[k + n + 1];
            pow26[0] = 1;
            long[] fact = new long[k + n + 1];
            long[] ifact = new long[k + n + 1];
            fact[0] = 1;
            ifact[0] = 1;
            for (int i = 1; i <= k + n; i++) {
                pow25[i] = pow25[i - 1] * 25 % mod;
                pow26[i] = pow26[i - 1] * 26 % mod;
                fact[i] = fact[i - 1] * i % mod;
                ifact[i] = ifact[i - 1] * modExp(i, mod - 2, mod) % mod;
            }
            for (int i = 0; i <= k; i++) {
                long add = pow26[i] * pow25[k - i] % mod * fact[n + k - i - 1] % mod * ifact[n - 1] % mod * ifact[k - i] % mod;
                res = (res + add) % mod;
            }
            w.println(res);
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.SpaceCharFilter filter;

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

        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public String nextString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                if (Character.isValidCodePoint(c)) {
                    res.appendCodePoint(c);
                }
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next() {
            return nextString();
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }

    }
}