#include<bits/stdc++.h>
#define int long long
//#define int __int128
#define ll long long
#define pa pair<int,int>
//#define int unsigned long long
#define sg signed
#define fi first
#define se second
#define ls s[x][0]
#define rs s[x][1]
#define ld long double
#define bs basic_string
const int inf=1e18;
const int mod=1e9+7;
using namespace std;
inline int read(){
    int s=0,w=1;
    char ch=getchar();
    while(ch<'0'||ch>'9') {
        if(ch=='-')w=-1;
        ch=getchar();
    }
    while(ch<='9'&&ch>='0')
        s=s*10+ch-'0',ch=getchar();
    return s*w;
}
int n,m,dp[155][30005][2];
int get(int x){
	return x*(x+1)/2;
}
int mi(int x,int y){
	int ans=1,base=x;
	while(y){
		if(y&1)ans=(ans*base)%mod;
		base=(base*base)%mod;
		y>>=1;
	}
	return ans;
}
void solve(){
	n=read(),m=read();
	dp[0][0][0]=1;
	for(int i=1;i<=n+1;i++){
		if(i==m)continue;
		for(int j=0;j<=n*n;j++)for(int k=0;k<i;k++){
			for(int op:{0,1})dp[i][j+get(i-k-1)][op]=(dp[i][j+get(i-k-1)][op]-dp[k][j][op])%mod;
			dp[i][j+get(i-k-1)][1]=(dp[i][j+get(i-k-1)][1]-dp[k][j][0]*(i-k-1-(k<m&&i>m)))%mod;
		}
	}
	int ans=0;
	for(int i=0;i<=n*n;i++){
//		cout<<i<<" "<<dp[n+1][i][1]<<endl;
		ans=(ans+dp[n+1][i][1]*mi((1-i*mi(get(n),mod-2))%mod,mod-2))%mod;
	}
	cout<<(ans*mi(n-1,mod-2)%mod+mod)%mod;
}
signed main(){
	int t=1;while(t--)solve();
    return 0;
}