# dp[i][j] : i番目まで見て
# j = 0 ... xxx
# j = 1 ... xxc
# j = 2 ... xco
# j = 3 ... con

mod = 998244353
n = int(input())
dp = [[0] * 4 for i in range(n+1)]
dp[0][0] = 1
ans = 0
for i in range(n):
	dp[i+1][1] = dp[i][0] + dp[i][1] * 25 + dp[i][3]
	dp[i+1][2] = dp[i][1] + dp[i][2] * 25
	dp[i+1][3] = dp[i][2]
	dp[i+1][0] = dp[i][0] * 25 + dp[i][3] * 25
	dp[i+1][1] %= mod
	dp[i+1][2] %= mod
	dp[i+1][0] %= mod
	ans += dp[i+1][3] * pow(26, n-i-1, mod)
	ans %= mod
print(ans)
#print(*dp)