#include //#include using namespace std; //using namespace atcoder; //using mint = modint1000000007; //const int mod = 1000000007; //using mint = modint998244353; //const int mod = 998244353; //const int INF = 1e9; //const long long LINF = 1e18; #define rep(i, n) for (int i = 0; i < (n); ++i) #define rep2(i,l,r)for(int i=(l);i<(r);++i) #define rrep(i, n) for (int i = (n-1); i >= 0; --i) #define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i) #define all(x) (x).begin(),(x).end() #define allR(x) (x).rbegin(),(x).rend() #define endl "\n" #define P pair template inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; } template inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; } int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int n, m; cin >> n >> m; if ((n < m) || (0 == m)) { cout << 0 << endl; return 0; } vector>v(n); v[0] = { 0,1 }; rep(i, n - 1) { // *(x-(i+1)) v[i + 1].resize(i + 3); rep(j, v[i].size()) { v[i + 1][j] -= v[i][j] * (i + 1); v[i + 1][j + 1] += v[i][j]; } } vectorans(n); vectordp(n + 1); dp[n] = 1; rrep(i, n) { long long x = dp[i + 1]; rep(j, v[i].size()) { dp[j] -= x * v[i][j]; } ans[i] = x; } long long val = ans[m - 1]; rep2(i, 1, m + 1) { val *= i; } cout << val << endl; return 0; }