#include<bits/stdc++.h>

template <int MOD_> struct modnum {
	static constexpr int MOD = MOD_;
	static_assert(MOD_ > 0, "MOD must be positive");

private:
	using ll = long long;

	int v;

	static int minv(int a, int m) {
		a %= m;
		assert(a);
		return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
	}

public:

	modnum() : v(0) {}
	modnum(ll v_) : v(int(v_ % MOD)) { if (v < 0) v += MOD; }
	explicit operator int() const { return v; }
	friend std::ostream& operator << (std::ostream& out, const modnum& n) { return out << int(n); }
	friend std::istream& operator >> (std::istream& in, modnum& n) { ll v_; in >> v_; n = modnum(v_); return in; }

	friend bool operator == (const modnum& a, const modnum& b) { return a.v == b.v; }
	friend bool operator != (const modnum& a, const modnum& b) { return a.v != b.v; }

	modnum inv() const {
		modnum res;
		res.v = minv(v, MOD);
		return res;
	}
	friend modnum inv(const modnum& m) { return m.inv(); }
	modnum neg() const {
		modnum res;
		res.v = v ? MOD-v : 0;
		return res;
	}
	friend modnum neg(const modnum& m) { return m.neg(); }

	modnum operator- () const {
		return neg();
	}
	modnum operator+ () const {
		return modnum(*this);
	}

	modnum& operator ++ () {
		v ++;
		if (v == MOD) v = 0;
		return *this;
	}
	modnum& operator -- () {
		if (v == 0) v = MOD;
		v --;
		return *this;
	}
	modnum& operator += (const modnum& o) {
		v += o.v;
		if (v >= MOD) v -= MOD;
		return *this;
	}
	modnum& operator -= (const modnum& o) {
		v -= o.v;
		if (v < 0) v += MOD;
		return *this;
	}
	modnum& operator *= (const modnum& o) {
		v = int(ll(v) * ll(o.v) % MOD);
		return *this;
	}
	modnum& operator /= (const modnum& o) {
		return *this *= o.inv();
	}

	friend modnum operator ++ (modnum& a, int) { modnum r = a; ++a; return r; }
	friend modnum operator -- (modnum& a, int) { modnum r = a; --a; return r; }
	friend modnum operator + (const modnum& a, const modnum& b) { return modnum(a) += b; }
	friend modnum operator - (const modnum& a, const modnum& b) { return modnum(a) -= b; }
	friend modnum operator * (const modnum& a, const modnum& b) { return modnum(a) *= b; }
	friend modnum operator / (const modnum& a, const modnum& b) { return modnum(a) /= b; }
};

template <typename T> T pow(T a, long long b) {
	assert(b >= 0);
	T r = 1; while (b) { if (b & 1) r *= a; b >>= 1; a *= a; } return r;
}

int main() {
	using namespace std;
	ios_base::sync_with_stdio(false), cin.tie(nullptr);

	using num = modnum<int(1e9)+7>;

	int N, A, B; cin >> N >> A >> B;
	assert(A <= N && B <= N);
	if (A > B) swap(A, B);
	assert(A <= B);

	// with bounding 1's
	vector<num> bways(N+3);
	bways[1] = 1;
	for (int i = 1; i+1 < int(bways.size()); i++) {
		bways[i+1] += bways[i];
		for (int j = A; i + j + 1 < int(bways.size()); j++) {
			bways[i+j+1] += bways[i];
		}
	}

	vector<array<num, 2>> totWays(N+3);
	for (int j = 1; j-1 < B; j++) {
		totWays[j][0] = bways[j];
	}
	for (int i = 0; i < N+2; i++) {
		for (int j = 1; i+j <= N+2 && j < A; j++) {
			totWays[i+j][1] += totWays[i][0];
		}
		for (int j = 1; i+j <= N+2 && j < B; j++) {
			totWays[i+j][0] += totWays[i][1] * bways[j];
		}
		if (i + B == N+2) {
			totWays[i+B][0] += totWays[i][1] * bways[B];
		}
	}

	cout << pow(num(2), N) - totWays[N+2][0] << '\n';

	return 0;
}


Measured memory_bytes: 3720