Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys

MOD = 998244353  # type: int

def combination(n: int, r:int, mod=MOD):
    n1 = n+1
    r = min(r, n-r)
    numer = denom = 1
    for i in range(1, r+1):
        numer = numer * (n1-i) % mod
        denom = denom * i % mod
    return numer * pow(denom, mod-2, mod) % mod


def solve(N: int, M: int, K: int):
    ans = 0
    for k in range(K+1): 
        ans += combination(N-1,N-k-1) * M * pow(M-1, N-k-1, MOD) % MOD
        ans %= MOD
    
    print(ans)

    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, M, K)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys

MOD = 998244353  # type: int


MAX = 600000
fac = [0] * MAX
ifac = [0] * MAX
fac[0] = 1
for i in range(1,MAX):
    fac[i] = (fac[i-1] * i) % MOD
ifac[MAX-1] = pow(fac[MAX-1],MOD-2,MOD)
for i in reversed(range(1,MAX)):
    ifac[i-1] = (ifac[i] * i) % MOD
 
def combination(n, k):
    if k < 0 or n < k:
        return 0
    else:
        return (fac[n] * ifac[k] * ifac[n-k]) % MOD

def solve(N: int, M: int, K: int):
    ans = 0
    for k in range(K+1): 
        ans += combination(N-1,N-k-1) * M * pow(M-1, N-k-1, MOD) % MOD
        ans %= MOD
    
    print(ans)

    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, M, K)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys

MOD = 998244353  # type: int

def combination(n: int, r:int, mod=MOD):
    n1 = n+1
    r = min(r, n-r)
    numer = denom = 1
    for i in range(1, r+1):
        numer = numer * (n1-i) % mod
        denom = denom * i % mod
    return numer * pow(denom, mod-2, mod) % mod


def solve(N: int, M: int, K: int):
    ans = 0
    for k in range(K+1): 
        ans += combination(N-1,N-k-1) * M * pow(M-1, N-k-1, MOD) % MOD
        ans %= MOD
    
    print(ans)

    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, M, K)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys

MOD = 998244353  # type: int


MAX = 600000
fac = [0] * MAX
ifac = [0] * MAX
fac[0] = 1
for i in range(1,MAX):
    fac[i] = (fac[i-1] * i) % MOD
ifac[MAX-1] = pow(fac[MAX-1],MOD-2,MOD)
for i in reversed(range(1,MAX)):
    ifac[i-1] = (ifac[i] * i) % MOD
 
def combination(n, k):
    if k < 0 or n < k:
        return 0
    else:
        return (fac[n] * ifac[k] * ifac[n-k]) % MOD

def solve(N: int, M: int, K: int):
    ans = 0
    for k in range(K+1): 
        ans += combination(N-1,N-k-1) * M * pow(M-1, N-k-1, MOD) % MOD
        ans %= MOD
    
    print(ans)

    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    solve(N, M, K)

if __name__ == '__main__':
    main()