#include <cstdio>
#include <utility>
#include <iostream>
using namespace std;

typedef long long ll;
const int mod = 1e9 + 7;

ll fastpow(ll b,ll e)
{
	if (e == 0)return 1;
	ll x = fastpow(b, e / 2);
	x = x * x % mod;
	if (e % 2)x =x*b%mod;
	return x;
}


int main()
{
	int n, a, b;
	cin >> n >> a >> b;
	ll ans = fastpow(2, n) - 1;
	ll ret = 1;
	for (int i = 0; i < a; i++) {
		ret *= 1LL*(n - i) * fastpow(i + 1, mod - 2) % mod;
		ret %= mod;
	}
	ans -= ret;
	ret = 1;
	for (int i = 0; i < b; i++) {
		ret *= 1LL*(n - i) * fastpow(i + 1, mod - 2) % mod;
		ret %= mod;
	}
	ans -= ret;
	ans = (ans % mod + mod) % mod;
	cout << ans;

}