#include <iostream> #include <vector> #include <algorithm> #include <cmath> #include <queue> #include <string> #include <map> #include <set> #include <stack> #include <tuple> #include <deque> #include <array> #include <numeric> #include <bitset> #include <iomanip> #include <cassert> #include <chrono> #include <random> #include <limits> #include <iterator> #include <functional> #include <sstream> #include <fstream> #include <complex> #include <cstring> #include <unordered_map> #include <unordered_set> using namespace std; using ll = long long; constexpr int INF = 1001001001; // constexpr int mod = 1000000007; constexpr int mod = 998244353; template<class T> inline bool chmax(T& x, T y){ if(x < y){ x = y; return true; } return false; } template<class T> inline bool chmin(T& x, T y){ if(x > y){ x = y; return true; } return false; } int main(){ ios::sync_with_stdio(false); cin.tie(nullptr); int N, K; cin >> N >> K; vector<bool> used(N + 1); int ans = 0; used[K] = true; auto dfs = [&](auto&& self, int x, int c = 1, bool f = false) -> void { if(c == N){ ans += f; return; } if(!f){ for(int i = 1; i < x; ++i){ if(!used[i]){ used[i] = true; self(self, i, c + 1, true); used[i] = false; break; } } } for(int i = x + 1; i <= N; ++i){ if(used[i]) continue; used[i] = true; self(self, i, c + 1, f); used[i] = false; } }; dfs(dfs, K); cout << ans << endl; return 0; }