#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define SZ(a) ((int)a.size())
#define ALL(v) v.begin(), v.end()
#define pb push_back

const int MOD = 998244353;
const int MAXC = 1 << 20;

void add(int &x, int val) {
    x += val;
    if (x >= MOD) x -= MOD;
}

int pw(int a, int n) {
    int rt = 1;
    for (; n; n >>= 1, a = (ll)a * a % MOD)
        if (n & 1)
            rt = (ll)rt * a % MOD;
    return rt;
}

template<int MAXN, ll P, ll RT> //MAXN must be 2^k
struct NTT {
    ll w[MAXN];
    ll mpow(ll a, ll n) {
        return pw(a, n);
    }
    ll minv(ll a) { return mpow(a, P - 2); }
    NTT() {
        ll dw = mpow(RT, (P - 1) / MAXN);
        w[0] = 1;
        for (int i = 1; i < MAXN; ++i) w[i] = w[i - 1] * dw % P;
    }
    void bitrev(ll *a, int n) {
        int i = 0;
        for (int j = 1; j < n - 1; ++j) {
            for (int k = n >> 1; (i ^= k) < k; k >>= 1);
            if (j < i) swap(a[i], a[j]);
        }
    }
    void operator()(ll *a, int n, bool inv = false) { //0 <= a[i] < P
        bitrev(a, n);
        for (int L = 2; L <= n; L <<= 1) {
            int dx = MAXN / L, dl = L >> 1;
            for (int i = 0; i < n; i += L) {
                for (int j = i, x = 0; j < i + dl; ++j, x += dx) {
                    ll tmp = a[j + dl] * w[x] % P;
                    if ((a[j + dl] = a[j] - tmp) < 0) a[j + dl] += P;
                    if ((a[j] += tmp) >= P) a[j] -= P;
                }
            }
        }
        if (inv) {
            reverse(a + 1, a + n);
            ll invn = minv(n);
            for (int i = 0; i < n; ++i) a[i] = a[i] * invn % P;
        }
    }
};

NTT<MAXC, MOD, 3> ntt;

int fac[MAXC + 5], ifac[MAXC + 5];

void build() {
    fac[0] = 1;
    for (int i = 1; i <= MAXC; ++i)
        fac[i] = (ll)fac[i - 1] * i % MOD;
    ifac[MAXC] = pw(fac[MAXC], MOD - 2);
    for (int i = MAXC - 1; i >= 0; --i)
        ifac[i] = (ll)ifac[i + 1] * (i + 1) % MOD;
}

ll arr[MAXC];

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int n, m;
    build();
    cin >> n >> m;
    for (int i = 0; i <= m; ++i)
        arr[i] = (ll)fac[m] * ifac[m - i] % MOD * fac[m] % MOD * ifac[m - i] % MOD * ifac[i] % MOD;
    ntt(arr, MAXC);
    for (int i = 0; i < MAXC; ++i)
        arr[i] = pw(arr[i], n);
    ntt(arr, MAXC, true);
    int ans = 0;
    for (int i = 0; i <= n * m; ++i) {
        int cur = (ll)arr[i] * fac[n * m - i] % MOD;
        if (i & 1) add(ans, MOD - cur);
        else add(ans, cur);
    }
    cout << ans << "\n";
}