#include <algorithm>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <clocale>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <limits>
#include <list>
#include <map>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <utility>
#include <vector>
#include <cwchar>
#include <cwctype>
#include <complex.h>
#include <fenv.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stdint.h>
#include <tgmath.h>
#include <string.h>
#include <math.h>
#include <stdio.h>
#define int long long
using namespace std;
const int N=1e5+10;
const int INF=0x3f3f3f3f;
int n,m,sum;
bool sb[N];
void dfs(int s,int a)
{
	if(a==0)
	{
		sum++;
		return;
	}
	if((n-s+1)/2<a)
		return;
	for(int i=s+2;i<=n;i++)
	{
		if(sb[i]==0)
		{
			sb[i]=1;
			dfs(i,a-1);
			sb[i]=0;
		}
	}
}
signed main()
{
	cin>>n>>m;
	dfs(-1,m);
	cout<<sum;
    return 0;
}

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e5+10;
const int INF=0x3f3f3f3f;
int n,m,ans;
bool v[N];
void dfs(int num,int c){
	if(c==0){
		ans++;
		return;
	}
	if((n-num+1)/2<c){
		return;
	}
	for(int i=num+2;i<=n;i++){
		if(v[i]==0){
			v[i]=1;
			dfs(i,c-1);
			v[i]=0;
		}
	}
}
signed main(){
	cin>>n>>m;
	dfs(-1,m);
	cout<<ans;
    return 0;
}

#include<iostream>
using namespace std;
const int MAXN = 1e5 + 10;
int n,m,ans;
void f(int n,int m) {
	if (n / 2 + 1 < m) {
		return ;
	}
	if (m == 0) {
		ans++;
		return ;
	}
	for (int i = n;i >= 1;i--) {
		f(i - 2,m - 1);
	}
}
int main() {
	cin >> n >> m;
	f(n,m);
	cout << ans << endl;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
const int N=1e2+10;
const int INF=0x3f3f3f3f;
int n,m,ans;
void f(int n,int m){
	if(n/2+1<m){
		return;
	}
	if(m==0){
		ans++;
		return;
	}
	for(int i=n;i>=1;i--){
		f(i-2,m-1);
	}
}
int main(){
	cin>>n>>m;
	f(n,m);
	cout<<ans;
	return 0;
}

#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int n,m,ans;
void f(int last,int step)
{
	if(last/2+1<step)
		return;
	if( 0 == step)
	{
		ans++;
		return ;
	}
	for(int i =last;i >=1;i--)
		f(i-2,step - 1);
}
int main()
{
	cin >> n >> m;
	f(n,m);
	cout<< ans<<endl;
	return 0;
}

/*****************************************
备注：
******************************************/
#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int n,m,ans;
void f(int last,int step)
{
	if(last/2+1<step)
		return;
	if(0==step)
	{
		ans++;
		return;
	}
	for(int i=last;i>=1;i--)
		f(i-2,step-1);
}
int main()
{
	cin>>n>>m;
	f(n,m);
	cout<<ans<<endl;
	return 0;
}

C++

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <math.h>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <stack>

using namespace std;

#define LL long long
const int N =1e5+10;
const int INF =0x3f3f3f3f;
int n,m,ans;
void f(int last ,int step){
	if(last/2+1<step)
		return;
	if(0== step){
		ans++;
		return;
	}
	for(int i=last;i>=1;i--)
		f(i-2,step-1);
}
int main(){
	cin>>n>>m;
	f(n,m);
	cout<<ans<<endl; 
	return 0;
}

C++
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <math.h>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <stack>

using namespace std;

#define LL long long
const int N =1e5+10;
const int INF =0x3f3f3f3f;
int n,m,ans;
void f(int last ,int step){
	if(last/2+1<step)
		return;
	if(0== step){
		ans++;
		return;
	}
	for(int i=last;i>=1;i--)
		f(i-2,step-1);
}
int main(){
	cin>>n>>m;
	f(n,m);
	cout<<ans<<endl; 
	return 0;
}

/*****************************************
备注：
******************************************/
#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int n,m,ans;
void f(int last,int step)
{
	if(last/2+1<step)
		return;
	if(0==step)
	{
		ans++;
		return;
	}
	for(int i=last;i>=1;i--)
		f(i-2,step-1);
}
int main()
{
	cin>>n>>m;
	f(n,m);
	cout<<ans<<endl;
	return 0;
}