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 PyPy3 (7.3.0) (judge verdict: Accepted)

#import sys
#import numpy as np
import math
#import itertools
#from fractions import Fraction
#import itertools
from collections import deque
from collections import Counter
#import heapq
#from fractions  import gcd
#input=sys.stdin.readline
#import bisect

Mod=10**9+7
M=10**6*2 #書き換え
fac=[0]*M
finv=[0]*M
inv=[0]*M

#finvに逆元、facに階乗のmod
def COMinit():
  fac[0]=fac[1]=1
  finv[0]=finv[1]=1
  inv[1]=1
  for i in range(2,M):
    fac[i]=(fac[i-1]*i%Mod)%Mod
    inv[i]=Mod-inv[Mod%i]*(Mod//i) %Mod
    finv[i]=(finv[i-1]*inv[i]%Mod)%Mod
def COM(n,k):
  if n<k:
    return 0
  if n<0 or k<0:
    return 0
  return (fac[n]*(finv[k]*finv[n-k]%Mod)%Mod)%Mod

COMinit()

k=int(input())
s=input()
n=len(s)
ans=0
for i in range(k+1):
    ans+=COM(n+k-i-1,n-1)*pow(26,i,Mod)*pow(25,k-i,Mod)
    ans=ans%Mod
print(ans)