import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.traits;
import std.functional;

pure nothrow @nogc
T gcdext(T) (T a, T b, ref T x, ref T y) {
  if (!b) {
    x = 1;
    y = 0;
    return a;
  }
  T res = gcdext (b, a % b, y, x);
  y -= x * (a / b);
  return res;
}

pure
X genericPower(alias mul, X, Y) (X x, Y y, X one = 1.to!X)
  if (isUnsigned!Y) {
  X a = one, b = x;
  while (y > 0) {
    if (y & 1) {
      a = binaryFun!mul (a, b);
    }
    b = binaryFun!mul (b, b);
    y >>>= 1;
  }
  return a;
}


struct IntM(int q = 1_000_000_007) {
  alias N = IntM!q;
  private:
  int v;
  invariant () { assert (v >= 0 && v < q); }
  pure nothrow @nogc
  static int from(T) (const T m) if (isIntegral!T) {
    int v = m % q;
    static if (isSigned!T) {
      if (v < 0) {
        v += q;
      }
    }
    return v;
  }
  public:
  pure nothrow @nogc
  this(T) (const T m) if (isIntegral!T) {
    v = from!T (m);
  }
  pure nothrow @nogc
  N opAssign(T) (const T m) if (isIntegral!T) {
    v = from!T (m);
    return this;
  }
  pure nothrow @nogc
  N opUnary (string op : "-")() const {
    return N (-v);
  }
  pure nothrow @nogc
  ref N opUnary (string op : "++")() {
    if (++v >= q) {
      v -= q;
    }
    return this;
  }
  pure nothrow @nogc
  ref N opUnary (string op : "--")() {
    if (--v < 0) {
      v += q;
    }
    return this;
  }
  pure nothrow @nogc
  ref N opOpAssign (string op : "+")(in N rhs) {
    v = (v + rhs.v) % q;
    return this;
  }
  pure nothrow @nogc
  ref N opOpAssign (string op : "-")(in N rhs) {
    v = (v - rhs.v + q) % q;
    return this;
  }
  pure nothrow @nogc
  ref N opOpAssign (string op : "*")(in N rhs) {
    v = (v.to!(long) * rhs.v) % q;
    return this;
  }
  pure nothrow @nogc
  ref N opOpAssign (string op : "/")(in N rhs) {
    return this *= rhs.inversion ();
  }
  pure nothrow @nogc
  ref N opOpAssign (string op)(in int rhs) if (op == "+" || op == "-" || op == "*" || op == "/") {
    mixin ("return this " ~ op ~ "= N(rhs);");
  }
  pure nothrow @nogc
  N opBinary (string op)(in N rhs) const if (op == "+" || op == "-" || op == "*" || op == "/") {
    N t = this;
    mixin ("t " ~ op ~ "= rhs;");
    return t;
  }
  pure nothrow @nogc
  N opBinary(string op,T)(const T rhs) const if (isIntegral!T && (op == "+" || op == "-" || op == "*" || op == "/")) {
    mixin ("return this " ~ op ~ " N(rhs);");
  }
  pure nothrow @nogc
  N opBinaryRight(string op,T)(const T rhs) const if (isIntegral!T && (op == "+" || op == "*")) {
    mixin ("return this " ~ op ~ " N(rhs);");
  }
  pure nothrow @nogc
  N inversion () const {
    int x, y;
    immutable g = gcdext!int (v, q, x, y);
    assert (g == 1);
    return N (x);
  }
  pure nothrow @nogc
  N opBinary (string op : "^^")(in ulong rhs) const {
    return genericPower! ("a * b", N, ulong) (this, rhs);
  }
  pure nothrow @nogc
  int opCast(T : int)() const { return v; }
  pure nothrow @nogc
  int opCmp (const N rhs) const {
    if (v < rhs.v) {
      return -1;
    }
    if (v > rhs.v) {
      return 1;
    }
    return 0;
  }
  pure nothrow
  string toString() const { return v.text; }
}

alias N = IntM!1_000_000_007;

auto binomial (int n, int k) {
  auto a = N (1);
  auto b = N (1);
  auto c = N (n);
  auto d = N (0);
  foreach (i; 0 .. k) {
    a *= c; --c;
    ++d;
    b *= d;
  }
  return a / b;
}

void main() {
  int n, a, b;
  readf (" %d %d %d", &n, &a, &b);
  auto r = N(2) ^^ n;
  --r;
  r -= binomial (n, a);
  r -= binomial (n, b);
  writeln (r);
}



Measured memory_bytes: 256