1 #include<iostream>
 2 #include<cstring>
 3 using namespace std;
 4 
 5 typedef long long ll;
 6 ll solve(int n,int k){
 7     if(n<k)return 0;
 8     if(n==k||k==1)return 1;
 9     return solve(n-1,k-1)+solve(n-1,k)*k;
10 }
11 int main(){
12     int n,k;
13     cin>>n>>k;
14     cout<<solve(n,k);
15     return 0;
16 }