#pragma GCC optimize("Ofast")
#include <cassert>
#include <iostream>
#include <algorithm>
#include <functional>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <complex>
#include <iomanip>
#include <bitset>
#include <random>

using namespace std;
using i64 = int_fast64_t;
using db = double;
using ldb = long double;
using pii = pair<int, int>;
using pli = pair<int_fast64_t, int>;
using pll = pair<int_fast64_t, int_fast64_t>;
using pdi = pair<double, int>;
using pdd = pair<double, double>;
template <class T> using vct = vector<T>;
template <class T> using heap = priority_queue<T>;
template <class T> using minheap = priority_queue<T, vector<T>, greater<T>>;
template <class T> constexpr T inf = numeric_limits<T>::max() / (T)1024;
constexpr int dx[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
constexpr int dy[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr long double Pi = 3.1415926535897932384626433832795028841971;
constexpr long double Golden = 1.61803398874989484820;
constexpr long double eps = 1e-15;

#define iostream_untie true
#define mod 1000000007LL
#define stdout_precision 10
#define stderr_precision 6
#define itrep(i,v) for(auto i = begin(v); i != end(v); ++i)
#define ritrep(i,v) for(auto i = rbegin(v); i != rend(v); ++i)
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
#define fir first
#define sec second
#define u_map unordered_map
#define u_set unordered_set
#define l_bnd lower_bound
#define u_bnd upper_bound
#define rsz resize
#define ers erase
#define emp emplace
#define emf emplace_front
#define emb emplace_back
#define pof pop_front
#define pob pop_back
#define mkp make_pair
#define mkt make_tuple
#define popcnt __builtin_popcount

namespace setup {
    struct setupper {
        setupper() {
            if(iostream_untie) {
                ios::sync_with_stdio(false);
                std::cin.tie(nullptr);
                std::cout.tie(nullptr);
                std::cerr.tie(nullptr);
            }
            std::cout << fixed << setprecision(stdout_precision);
            std::cerr << fixed << setprecision(stderr_precision);
    #ifdef LOCAL
            if(!freopen("input.txt","rt",stdin)) {
                cerr << "Failed to open the input file.\n"; exit(EXIT_FAILURE);
            }
            // if(!freopen("output.txt","wt",stdout)) {
            //     cerr << "Failed to open the output file.\n"; exit(EXIT_FAILURE);
            // }
            // std::cerr << "\n---stderr---\n";
            // auto print_atexit = []() {
            //     std::cerr << "Exec time : " << clock() / (double)CLOCKS_PER_SEC * 1000.0 << "ms\n";
            //     std::cerr << "------------\n";
            // };
            // atexit((void(*)())print_atexit);
            // atexit((void(*)())fclose(stdin));
    #endif
        }
    } __setupper;
}

namespace std {
    template <class RAitr> void rsort(RAitr __first, RAitr __last) {
        sort(__first, __last, greater<>());
    }
    template <class T> void hash_combine(size_t &seed, T const &key) {
        seed ^= hash<T>()(key) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
    }
    template <class T, class U> struct hash<pair<T,U>> {
        size_t operator()(pair<T,U> const &pr) const
        {
            size_t seed = 0;
            hash_combine(seed,pr.first);
            hash_combine(seed,pr.second);
            return seed;
        }
    };
    template <class Tup, size_t index = tuple_size<Tup>::value - 1> struct hashval_calc {
        static void apply(size_t& seed, Tup const& tup) {
            hashval_calc<Tup, index - 1>::apply(seed, tup);
            hash_combine(seed,get<index>(tup));
        }
    };
    template <class Tup> struct hashval_calc<Tup,0> {
        static void apply(size_t& seed, Tup const& tup) {
            hash_combine(seed,get<0>(tup));
        }
    };
    template <class ...T> struct hash<tuple<T...>> {
        size_t operator()(tuple<T...> const& tup) const
        {
            size_t seed = 0;
            hashval_calc<tuple<T...>>::apply(seed,tup);
            return seed;
        }
    };
}

template <class T, class U> istream &operator>> (istream &s, pair<T,U> &p) { return s >> p.first >> p.second; }
template <class T, class U> ostream &operator<< (ostream &s, const pair<T,U> p) { return s << p.first << " " << p.second; }
template <class T> ostream &operator<< (ostream &s, const vector<T> &v) {
    for(size_t i = 0; i < v.size(); ++i) s << (i ? " " : "") << v[i]; return s;
}
#define dump(...) cerr << " [ " << __LINE__ << " : " << __FUNCTION__ << " ] " << #__VA_ARGS__ << " : ";\
dump_func(__VA_ARGS__)
template <class T> void dump_func(T x) { cerr << x << '\n'; }
template <class T,class ...Rest> void dump_func(T x, Rest ... rest) { cerr << x << ","; dump_func(rest...); }
template <class T = i64> T read() { T x; return cin >> x, x; }
template <class T> void write(T x) { cout << x << '\n'; }
template <class T, class ...Rest> void write(T x, Rest ... rest) { cout << x << ' '; write(rest...); }
void writeln() {}
template <class T, class ...Rest> void writeln(T x, Rest ... rest) { cout << x << '\n'; writeln(rest...); }
#define esc(...) writeln(__VA_ARGS__), exit(0)

namespace updater {
    template <class T> static void add(T &x, const T &y) { x += y; }
    template <class T> static void ext_add(T &x, const T &y, size_t w) { x += y * w; }
    template <class T> static void mul(T &x, const T &y) { x *= y; }
    template <class T> static void ext_mul(T &x, const T &y, size_t w) { x *= (T)pow(y,w); }
    template <class T> static bool chmax(T &x, const T &y) { return x < y ? x = y,true : false; }
    template <class T> static bool chmin(T &x, const T &y) { return x > y ? x = y,true : false; }
};
using updater::add;
using updater::chmax;
using updater::chmin;

template <class T> constexpr T minf(const T &x, const T &y) { return min(x,y); }
template <class T> constexpr T maxf(const T &x, const T &y) { return max(x,y); }
constexpr bool bit(i64 n, int e) { return (n >> e) & 1; }
constexpr int_fast64_t mask(int_fast64_t n, int e) { return n & ((1 << e) - 1); }
constexpr int ilog(int_fast64_t x, int_fast64_t b = 2) { return x ? 1 + ilog(x / b, b) : -1; }
template <class F> int_fast64_t binry(int_fast64_t ok, int_fast64_t ng, const F &fn) {
    while (abs(ok - ng) > 1) {
        int_fast64_t mid = (ok + ng) / 2;
        (fn(mid) ? ok : ng) = mid;
    }
    return ok;
}
template <class A, size_t N, class T> void init(A (&array)[N], const T &val) { fill((T*)array,(T*)(array + N),val); }
template <class T> vector<int> cmprs(const vector<T> &v) {
    vector<T> tmp = v; vector<int> ret;
    sort(begin(tmp),end(tmp));
    tmp.erase(unique(begin(tmp),end(tmp)), end(tmp));
    for(T i : v) ret.emplace_back(lower_bound(begin(tmp),end(tmp),i) - begin(tmp));
    return ret;
}
template <class T> vector<int> cmprs(const T *__first, const T *__last) {
    return cmprs(vector<T>(__first, __last));
}
template <class F> void for_subset(uint_fast64_t s, const F &fn) {
    uint_fast64_t tmp = s;
    do { fn(tmp); } while((--tmp &= s) != s);
}


/* The main code follows. */

struct modint {
    int x;
    constexpr modint() : x(0) {}
    constexpr modint(int_fast64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

    constexpr modint &operator+=(const modint &p) {
        if((x += p.x) >= mod) x -= mod;
        return *this;
    }

    constexpr modint &operator ++() { return ++x,*this; }

    constexpr modint operator ++(int) {
        modint t = *this; 
        return ++x,t;
    }

    constexpr modint &operator-=(const modint &p) {
        if((x += mod - p.x) >= mod) x -= mod;
        return *this;
    }

    constexpr modint &operator --() { return --x,*this; }

    constexpr modint operator --(int) {
        modint t = *this;
        return --x,t;
    }

    constexpr modint &operator*=(const modint &p) {
        x = (int) (1LL * x * p.x % mod);
        return *this;
    }

    constexpr modint &operator/=(const modint &p) {
        *this *= inverse(p);
        return *this;
    }

    constexpr modint operator-() { return modint(-x); }

    constexpr modint operator+(const modint &p) { return modint(*this) += p; }

    constexpr modint operator-(const modint &p) { return modint(*this) -= p; }

    constexpr modint operator*(const modint &p) { return modint(*this) *= p; }

    constexpr modint operator/(const modint &p) { return modint(*this) /= p; }

    constexpr bool operator==(const modint &p) { return x == p.x; }

    constexpr bool operator!=(const modint &p) { return x != p.x; }

    constexpr bool operator!() { return !x; }

    constexpr bool operator>(const modint &p) { return x > p.x; }

    constexpr bool operator<(const modint &p) { return x <  p.x; }

    constexpr bool operator>=(const modint &p) { return x >= p.x; }

    constexpr bool operator<=(const modint &p) { return x <= p.x; }

    constexpr static modint inverse(const modint &p) {
        int a = p.x, b = mod, u = 1, v = 0;
        while(b > 0) {
            int t = a / b;
            a -= t * b;
            a ^= b ^= a ^= b;
            u -= t * v;
            u ^= v ^= u ^= v;
        }
        return modint(u);
    }

    constexpr static modint pow(modint p, uint_fast64_t e) {
        if(!e) return 1;
        return pow(p * p, e >> 1) * (e & 1 ? p : 1);
    }

    friend ostream &operator<<(ostream &s, const modint &p) { return s << p.x; }

    friend istream &operator>>(istream &s, modint &p) {
        uint_fast64_t x;
        p = modint((s >> x,x));
        return s;
    }
};

int n,k;
modint ans;
modint now[310][310],nxt[310][310];

signed main() {
    cin>>n>>k;
    for(int y=1; y<=k && y<=n; ++y) {
        now[y-1][y]=1;
    }
    for(int t=0; t<k; ++t) {
        for(int y=1; y<=k; ++y) {
            for(int x=0; x<y; ++x) {
                if(!now[x][y]) continue;
                if(x) {
                    nxt[x-1][y]+=now[x][y];
                    nxt[x][y]+=now[x][y]*(n-2);
                } else {
                    nxt[x][y]+=now[x][y]*(n-1);
                }
                nxt[x][y-1]+=now[x][y];
            }
        }
        swap(now,nxt);
        init(nxt,0);
    }
    for(int y=1; y<=k; ++y) {
        modint tmp=0;
        for(int x=0; x<y; ++x) {
            tmp+=now[x][y];
        }
        ans+=tmp*y;
    }
    if(n<=k) esc(ans);
    init(now,0);
    now[k][k+1]=1;
    for(int t=0; t<k; ++t) {
        for(int y=1; y<=k+1; ++y) {
            for(int x=0; x<y; ++x) {
                if(!now[x][y]) continue;
                if(x) {
                    nxt[x-1][y]+=now[x][y];
                    nxt[x][y]+=now[x][y]*(n-2);
                } else {
                    nxt[x][y]+=now[x][y]*(n-1);
                }
                nxt[x][y-1]+=now[x][y];
            }
        }
        swap(now,nxt);
        init(nxt,0);
    }
    for(int y=1; y<=k+1; ++y) {
        modint tmp=0;
        for(int x=0; x<y; ++x) {
            tmp+=now[x][y];
        }
        ans+=tmp*(n-k)*(y*2+n-k-1)/2;
    }
    esc(ans);
}