#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
int f[2][505][505], n, m;
const int mod = 998244353;
signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int now = 1, pre = 0;
	cin >> n >> m;
	f[pre][m][0] = 1;
	for (int i = 1; i <= n; i++, swap(now, pre)) {
		memset(f[now], 0, sizeof(f[now]));
		for (int j = 0; j <= m; j++) {
			for (int k = ((i == n) ? (0) : (1)); j + k <= m; k++) {
				f[now][j][k] = 1ll * f[pre][j][k] * k % mod;
				f[now][j][k] = (f[now][j][k] + 1ll * f[pre][j][k + 1] * (k + 1) % mod) % mod;
				if (k)	f[now][j][k] = (1ll * f[now][j][k] + f[pre][j + 1][k - 1] % mod) % mod;
				f[now][j][k] = (1ll * f[now][j][k] + f[pre][j + 1][k]  % mod) % mod;
			}
		}
	}
	cout << f[pre][0][0];
}