output_description: Print the number of strings satisfying the condition, modulo (10^9+7).
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      K
      S
attempt: mod = 1000000007
  fact = []
  fact_inv = []
  pow_ = []
  pow25_ = []
  pow26_ = []
  
  def pow_ini(nn):
  	global pow_
  	pow_.append(nn)
  	for j in range(62):
  		nxt = pow_[j] * pow_[j]
  		nxt %= mod
  		pow_.append(nxt)
  	return
  
  def pow1(k):
  	ansk = 1
  	for ntmp in range(62):
  		if((k >> ntmp) % 2 == 1):
  			ansk *= pow_[ntmp]
  			ansk %= mod
  	return ansk
  
  def fact_ini(n):
  	global fact
  	global fact_inv
  	global pow_
  	fact = [0] * (n+1)
  	fact_inv = [0] * (n+1)
  	fact[0] = 1
  	for i in range(1, n + 1, 1):
  		fact_tmp = fact[i - 1] * i
  		fact_tmp %= mod
  		fact[i] = fact_tmp
  	pow_ini(fact[n])
  	fact_inv[n] = pow1(mod - 2)
  	for i in range(n - 1, -1, -1):
  		fact_inv[i] = fact_inv[i + 1] * (i + 1)
  		fact_inv[i] %= mod
  	return
  
  def nCm(n, m):
  	ans = fact[n] * fact_inv[m]
  	ans %= mod
  	ans *= fact_inv[n - m]
  	ans %= mod
  	return ans;
  
  fact_ini(2200000)
  K = int(input())
  S = input()
  N = len(S)
  ans = 0
  
  ans25=[1] * (K+11)
  ans26=[1] * (K+11)
  
  for k in range(K+10):
  	ans25[k+1] = ans25[k] * 25
  	ans26[k+1] = ans26[k] * 26
  	ans25[k+1] %= mod
  	ans26[k+1] %= mod
  
  for k in range(0, K+1, 1):
  	n = N + K - k
  	anstmp = 1
  	anstmp *= ans26[k]
  	anstmp %= mod
  	anstmp *= nCm(n - 1, N - 1)
  	anstmp %= mod
  	anstmp *= ans25[n - N]
  	anstmp %= mod
  	ans += anstmp
  	ans %= mod
  print(ans)
problem_description: 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).
samples: [{"input": "5\n    oof", "output": "575111451\n    \n\nFor example, we can obtain `proofend`, `moonwolf`, and `onionpuf`, while we\ncannot obtain `oofsix`, `oofelevennn`, `voxafolt`, or `fooooooo`.\n\n* * *"}, {"input": "37564\n    whydidyoudesertme", "output": "318008117"}]