#include<bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define pb push_back
using namespace std;
const int N=55;
const int mod=1e9+7;
int n,m;
ll f[N][N*N][N],ifac[N*N],res;
int get(int x){
    return x*(x+1)/2;
}
ll fpow(ll x,ll y=mod-2){
    ll z(1);
    for(;y;y>>=1){
        if(y&1)z=z*x%mod;
        x=x*x%mod;
    }return z;
}
void init(int n){
    ifac[1]=1;for(int i=2;i<=n;i++)ifac[i]=mod-ifac[mod%i]*(mod/i)%mod;
}
int main(){
    //freopen("data.in","r",stdin);
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    cin>>n>>m,init(n*(n+1));
    if(n==2){
        cout<<0;
        return 0;
    }
    f[0][0][0]=1;
    for(int i=0;i<n;i++){
        for(int j=0;j<=i*(i+1)/2;j++){
            for(int k=0;k<=i;k++){
                if(!f[i][j][k])continue;
                for(int l=i+1;l<=n;l++){
                    (f[l][j+get(l-i-1)][k+1]-=f[i][j][k])%=mod;
                }
            }
        }
    }
    for(int i=0;i<=n-m;i++){
        for(int j=0;j<=i*(i+1)/2;j++){
            for(int k=0;k<=i;k++){
                if(!f[i][j][k])continue;
                for(int ti=0;ti<=m-1;ti++){
                    for(int tj=0;tj<=ti*(ti+1)/2;tj++){
                        for(int tk=0;tk<=ti;tk++){
                            if(!f[ti][tj][tk])continue;
                            int x=(n-m-i+1)*(m-1-ti+1)+j+tj+get(n-m-i)+get(m-1-ti);
                            int y=n*(n+1)/2-x;
                            if(!y)continue;
                            //cout<<"find:"<<i<<" "<<j<<" "<<k<<" "<<ti<<" "<<tj<<" "<<tk<<" "<<y<<" "<<f[i][j][k]*f[ti][tj][tk]<<"\n";
                            res=(res-f[i][j][k]*f[ti][tj][tk]%mod*ifac[y]%mod*(n-1-k-tk))%mod;
                        }
                    }
                }
            }
        }
    }
    res=res*fpow(n-1)%mod*n*(n+1)%mod*(mod+1>>1)%mod;
    cout<<(res+mod)%mod;
}