// Copyright (C) 2017 __debug.

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; version 3

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; If not, see <http://www.gnu.org/licenses/>.


#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>

#define x first
#define y second
#define MP std::make_pair
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#ifdef __linux__
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif

using std::pair;
using std::vector;
using std::string;

typedef long long LL;
typedef pair<int, int> Pii;

const int oo = 0x3f3f3f3f;

template<typename T> inline bool chkmax(T &a, T b) { return a < b ? a = b, true : false; }
template<typename T> inline bool chkmin(T &a, T b) { return b < a ? a = b, true : false; }
string procStatus()
{
    std::ifstream t("/proc/self/status");
    return string(std::istreambuf_iterator<char>(t), std::istreambuf_iterator<char>());
}
template<typename T> T read(T &x)
{
    int f = 1;
    char ch = getchar();
    for (; !isdigit(ch); ch = getchar())
        f = (ch == '-' ? -1 : 1);
    for (x = 0; isdigit(ch); ch = getchar())
        x = 10 * x + ch - '0';
    return x *= f;
}
template<typename T> void write(T x)
{
    if (x == 0) {
        putchar('0');
        return;
    }
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    static char s[20];
    int top = 0;
    for (; x; x /= 10)
        s[++top] = x % 10 + '0';
    while (top)
        putchar(s[top--]);
}
// EOT

const int MAXN = 4e3 + 5;
const int MOD = 1e9 + 7;

int N, K;

void input()
{
    read(N); read(K);
}

LL fpm(LL base, LL exp)
{
    LL ret = 1;
    for (; exp; exp >>= 1) {
        if (exp & 1)
            (ret *= base) %= MOD;
        (base *= base) %= MOD;
    }
    return ret;
}

LL fac[MAXN], ifac[MAXN], pow2[MAXN];

inline LL C(int n, int k)
{
    return n < k ? 0 : fac[n] * ifac[k] % MOD * ifac[n - k] % MOD;
}

void solve()
{
    int bnd = N * 2;
    fac[0] = 1;
    for (int i = 1; i <= bnd; ++i) {
        fac[i] = fac[i - 1] * i % MOD;
    }
    ifac[bnd] = fpm(fac[bnd], MOD - 2);
    for (int i = bnd; i >= 1; --i) {
        ifac[i - 1] = ifac[i] * i % MOD;
    }

    int ans = 0;
    if (K == 1)
        ans = 1;
    else for (int i = 0; i < K; ++i) {
        (ans += (C(K-2+i, K-2) - C(K-2+i, K-1) + MOD) * C(N-1-i, K-1-i) % MOD) %= MOD;
    }
    for (int i = 0; i < N - K - 1; ++i) {
        (ans *= 2) %= MOD;
    }

    printf("%d\n", ans);
}

int main()
{
#ifdef __DEBUG
    freopen("F.in", "r", stdin);
    freopen("F.out", "w", stdout);
#endif

    input();
    solve();

    return 0;
}

// 醉别西楼醒不记。春梦秋云，聚散真容易。
//     -- 晏几道《蝶恋花·醉别西楼醒不记》


Measured memory_bytes: 256