#include <iostream>
#include <numeric>
#include <vector>

template <class T>
T Vec(T v) { return v; }

template <class T, class... Ts>
auto Vec(size_t l, Ts... ts) {
    return std::vector<decltype(Vec<T>(ts...))>(l, Vec<T>(ts...));
}

class ModInt {
    using ll = long long;

public:
    int value;
    static int MOD;

    ModInt(ll value = 0) {
        this->value = (-MOD < value && value < MOD ? value : value % MOD);
        if (this->value < 0) this->value += MOD;
    }

    operator int() const noexcept { return this->value; }
    operator ll() const noexcept { return this->value; }

    ModInt& operator=(const ModInt& x) {
        if (this != &x) { this->value = x.value; }
        return *this;
    }

    bool operator==(const ModInt& x) const { return this->value == x.value; }
    bool operator!=(const ModInt& x) const { return !(*this == x); }

    ModInt operator+() const { return value; }
    ModInt operator-() const { return MOD - value; }
    ModInt operator~() const { return (*this) ^ ModInt(MOD - 2); }

    ModInt operator++() { return *this += 1; }
    ModInt operator--() { return *this -= 1; }

    ModInt operator++(int) {
        ModInt before = *this;
        ++(*this);
        return before;
    }
    ModInt operator--(int) {
        ModInt before = *this;
        --(*this);
        return before;
    }

    ModInt& operator+=(const ModInt& x) {
        int sum = this->value + x.value;
        return *this = (sum < MOD ? sum : sum - MOD);
    }
    ModInt& operator-=(const ModInt& x) {
        int diff = this->value - x.value;
        return *this = (diff >= 0 ? diff : diff + MOD);
    }
    ModInt& operator+=(int x) { return *this += ModInt(x); }
    ModInt& operator-=(int x) { return *this -= ModInt(x); }

    template <class T>
    ModInt& operator*=(const T& x) { return *this = ll(this->value) * ll(x) % MOD; }
    template <class T>
    ModInt& operator/=(const T& x) { return *this = (this->value % int(x) == 0 ? ModInt(this->value / int(x)) : *this * ~ModInt(x)); }
    template <class T>
    ModInt& operator^=(const T& x) {
        int n = int(x);
        ModInt b = *this;
        *this = 1;
        while (n > 0) {
            if (n & 1) *this *= b;
            n >>= 1;
            b *= b;
        }
        return *this;
    }

    template <class T>
    ModInt operator+(const T& b) const { return ModInt(*this) += b; }
    template <class T>
    ModInt operator-(const T& b) const { return ModInt(*this) -= b; }
    template <class T>
    ModInt operator*(const T& b) const { return ModInt(*this) *= b; }
    template <class T>
    ModInt operator/(const T& b) const { return ModInt(*this) /= b; }
    template <class T>
    ModInt operator^(const T& b) const { return ModInt(*this) ^= b; }
};

std::ostream& operator<<(std::ostream& os, const ModInt& x) { return os << x.value; }
std::istream& operator>>(std::istream& is, ModInt& x) { return is >> x.value; }

int ModInt::MOD = 1000000007;

int main() {
    int N, K;
    std::cin >> N >> K;

    auto dp = Vec<ModInt>(N + 1, K + 1, ModInt(0));
    // i個のボールをちょうどj個の集合に分ける

    dp[0][0] = 1;
    for (int i = 1; i <= N; ++i) {
        for (int j = 0; j <= K; ++j) {
            // i個目をどこかの集合に加える
            dp[i][j] += dp[i - 1][j] * j;
            // i個目を独立の集合にする
            if (j > 0) dp[i][j] += dp[i - 1][j - 1];
        }
    }

    std::cout << std::accumulate(dp[N].begin(), dp[N].end(), ModInt(0)) << std::endl;
}


Measured memory_bytes: 6744