Buggy python submission (verdict: Time Limit Exceeded):
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""


# def pw(a,b):
#     result=1
#     while(b>0):
#         if(b%2==1): result*=a
#         a*=a
#         b//=2
#     return result


def ncr(n, r, p):
    num = den = 1
    for i in range(r):
        num = (num * (n - i)) % p
        den = (den * (i + 1)) % p
    return (num * pow(den, p - 2, p)) % p


def inpt():
    return [int(k) for k in input().split()]


def main():
    k = int(input())
    s = input()
    n = len(s)
    ans = 0
    md = 10 ** 9 + 7
    ar26=[1]
    ar25=[1]
    a=1
    b=1
    for i in range(k):
        a*=25
        a%=md
        b*=26
        b%=md
        ar26.append(b)
        ar25.append(a)

    for i in range(k+1):
        ans+=(ncr(n+k-i-1,n-1,md)*ar26[i]*ar25[k-i])
        ans%=md
    print(ans)

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()


Fixed submission:
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""


# def pw(a,b):
#     result=1
#     while(b>0):
#         if(b%2==1): result*=a
#         a*=a
#         b//=2
#     return result



def inpt():
    return [int(k) for k in input().split()]


def main():
    k = int(input())
    s = input()
    n = len(s)
    ans = 0
    md = 10 ** 9 + 7
    ar26=[1]
    ar25=[1]
    a=1
    b=1
    nn=1
    rr=1
    num=[1]
    rum=[1]
    for i in range(1,n+k+1):
        nn*=i
        nn%=md
        rr*=i
        rr%=md
        num.append(nn)
        rum.append(rr)

    for i in range(k):
        a*=25
        a%=md
        b*=26
        b%=md
        ar26.append(b)
        ar25.append(a)

    for i in range(k+1):
        ans+=(num[n+k-i-1]*pow((rum[n-1]*rum[k-i])%md,md-2,md)*ar26[i]*ar25[k-i])
        ans%=md
    print(ans)

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""


# def pw(a,b):
#     result=1
#     while(b>0):
#         if(b%2==1): result*=a
#         a*=a
#         b//=2
#     return result


def ncr(n, r, p):
    num = den = 1
    for i in range(r):
        num = (num * (n - i)) % p
        den = (den * (i + 1)) % p
    return (num * pow(den, p - 2, p)) % p


def inpt():
    return [int(k) for k in input().split()]


def main():
    k = int(input())
    s = input()
    n = len(s)
    ans = 0
    md = 10 ** 9 + 7
    for i in range(k + 1):
        ans += (ncr(n + k - i - 1, n - 1, md) * (pow(26, i, md)) % md * pow(25, k - i, md)) % md
        ans %= md
    print(ans)


BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()


Fixed submission:
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""


# def pw(a,b):
#     result=1
#     while(b>0):
#         if(b%2==1): result*=a
#         a*=a
#         b//=2
#     return result



def inpt():
    return [int(k) for k in input().split()]


def main():
    k = int(input())
    s = input()
    n = len(s)
    ans = 0
    md = 10 ** 9 + 7
    ar26=[1]
    ar25=[1]
    a=1
    b=1
    nn=1
    rr=1
    num=[1]
    rum=[1]
    for i in range(1,n+k+1):
        nn*=i
        nn%=md
        rr*=i
        rr%=md
        num.append(nn)
        rum.append(rr)

    for i in range(k):
        a*=25
        a%=md
        b*=26
        b%=md
        ar26.append(b)
        ar25.append(a)

    for i in range(k+1):
        ans+=(num[n+k-i-1]*pow((rum[n-1]*rum[k-i])%md,md-2,md)*ar26[i]*ar25[k-i])
        ans%=md
    print(ans)

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase


"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""

"""def pw(a,b):
    result=1
    while(b>0):
        if(b%2==1): result*=a
        a*=a
        b//=2
    return result"""


def ncr(n, r, p):
    num = den = 1
    for i in range(r):
        num = (num * (n - i)) % p
        den = (den * (i + 1)) % p
    return (num * pow(den,p - 2, p)) % p


def inpt():
    return [int(k) for k in input().split()]


def main():
    k=int(input())
    s=input()
    n=len(s)
    ans=0
    md=10**9+7
    for i in range(k+1):
        ans+=(ncr(n+k-i-1,n-1,md) * (26**i)%md * 25**(k-i)%md )%md
    print(ans)















BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()


Fixed submission:
import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""


# def pw(a,b):
#     result=1
#     while(b>0):
#         if(b%2==1): result*=a
#         a*=a
#         b//=2
#     return result



def inpt():
    return [int(k) for k in input().split()]


def main():
    k = int(input())
    s = input()
    n = len(s)
    ans = 0
    md = 10 ** 9 + 7
    ar26=[1]
    ar25=[1]
    a=1
    b=1
    nn=1
    rr=1
    num=[1]
    rum=[1]
    for i in range(1,n+k+1):
        nn*=i
        nn%=md
        rr*=i
        rr%=md
        num.append(nn)
        rum.append(rr)

    for i in range(k):
        a*=25
        a%=md
        b*=26
        b%=md
        ar26.append(b)
        ar25.append(a)

    for i in range(k+1):
        ans+=(num[n+k-i-1]*pow((rum[n-1]*rum[k-i])%md,md-2,md)*ar26[i]*ar25[k-i])
        ans%=md
    print(ans)

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

if __name__ == "__main__":
    main()