#include<bits/stdc++.h>
#define int long long
#define i128 __int128
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rof(i,a,b) for(int i=(a);i>=(b);--i)
using namespace std;
const int Maxn=5e3,inf=1e18;

int n,m,C[Maxn+5][Maxn+5];

inline void Solve()
{
    m=min(m,n-m);
    if(m==0) {cout<<1<<endl; return;}
    if(m==1) {cout<<n<<endl; return;}
    if(m==2) {cout<<n*(n-1)/2<<endl; return;}
    if(n>=2000000) {cout<<inf<<endl; return;}
    if(m==3) {cout<<min(inf,n*(n-1)*(n-2)/6)<<endl; return;}
    if(n>=100000) {cout<<inf<<endl; return;}
    if(m==4)
    {
        i128 res=(i128)n*(n-1)*(n-2)*(n-3)/24;
        res=min(res,(i128)inf); cout<<(int)res<<endl; return;
    }
    if(n>=20000) {cout<<inf<<endl; return;}
    if(m==5)
    {
        i128 res=(i128)n*(n-1)*(n-2)*(n-3)*(n-4)/120;
        res=min(res,(i128)inf); cout<<(int)res<<endl; return;
    }
    if(n>=5000) {cout<<inf<<endl; return;}
    cout<<C[n][m]<<endl;
}

signed main()
{
    // freopen("1.in","r",stdin);

    C[0][0]=1;
    For(i,1,Maxn)
    {
        C[i][0]=1;
        For(j,1,i) C[i][j]=min(inf,C[i-1][j]+C[i-1][j-1]);
    }
    while(cin>>n>>m) Solve();
    return 0;
}