#include<bits/stdc++.h>
#define int long long
using namespace std;
const int MOD = 1e9 + 7;
int n,m,ans = 0;
int f[160][160 * 160][2];
int qpow(int a,int b){
	int res = 1;
	for( ; b; b >>= 1){
		if(b & 1) res = (res * a) % MOD;
		a = (a * a) % MOD;
	}
	return res;
}
int s(int x){
	return x * (x + 1) / 2;
}
signed main(){
	scanf("%lld %lld",&n,&m);
	f[0][0][0] = 1;
	for(int i = 0; i <= n; i++){
		if(i == m) continue;
		for(int j = 0; j <= n * (n + 1) / 2; j++){
			for(int p = i + 1; p <= n + 1; p++){
				(f[p][j + s(p - i - 1)][0] -= f[i][j][0]) %= MOD;
				(f[p][j + s(p - i - 1)][1] -= f[i][j][1]) %= MOD;
				(f[p][j + s(p - i - 1)][1] -= f[i][j][0] * (p - i - 1 - (i < m && m < p)) % MOD) %= MOD;
			}
		}
	}
	int ans = 0;
	for(int i = 0; i <= s(n); i++){
		int coef = s(n) % MOD * qpow(s(n) - i,MOD - 2) % MOD;
		(ans += coef * f[n + 1][i][1] % MOD) %= MOD; 
	}
	(ans *= qpow(n - 1,MOD - 2)) %= MOD;
	printf("%lld",(ans + MOD) % MOD);
	return 0;
}