#include <algorithm>
#include <iostream>
#include <vector>
#include <math.h>
#include <set>
#include <map>
#include <string>
#include <stack>
#include <queue>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <bitset>
#include <complex>
#include <unistd.h>
#include <cassert>
#include <cctype>
#include <random>
#include <time.h>
#include <functional>
#define _USE_MATH_DEFINES
#define _GLIBCXX_DEBUG
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> plglg;
typedef pair<double, ll> pdlg;
typedef tuple<int, int, int> tiii;
typedef tuple<ll, ll, ll> tlglglg;
typedef tuple<ll, ll, ll, ll> tlglglglg;
typedef tuple<double, double, double> tddd;
typedef complex<double> xy_t;
typedef vector<ll> vll;
typedef vector< vector<ll> > matrix;
typedef unsigned int uint;
typedef unsigned long long ull;
template <class T> using V = vector<T>;
template <class T> using VV = V<V<T>>;
template <class T> using VVV = V<VV<T>>;
#define REP(i, x, y) for(ll i = (ll)x; i < (ll)y; i++)
#define DREP(i, x, y, d) for(ll i = (ll)x; i < (ll)y; i += (ll)d)
#define PER(i, x, y) for(ll i = (ll)x; i > (ll)y; i--)
#define DPER(i, x, y, d) for(ll i = (ll)x; i > (ll)y; i -= (ll)d)
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
double pi = 3.141592653589793;
ll mod = 1000000007;
int intmax = 2147483647;
int intmin = -2147483648;
ll llmax = 9223372036854775807;
ll llmin = -9223372036854775807;
int iinf = intmax / 8;
ll inf = llmax / 8;
double eps = 1e-12;
void yesno(bool ok, string yes = "Yes", string no = "No") {
    if (ok) {
        cout << yes << endl;
    } else {
        cout << no << endl;
    }
}

template <uint MD> struct ModInt {
    using M = ModInt;
    const static M G;
    uint v;
    ModInt(ll _v = 0) { set_v(uint(_v % MD + MD)); }
    M& set_v(uint _v) {
        v = (_v < MD) ? _v : _v - MD;
        return *this;
    }
    explicit operator bool() const { return v != 0; }
    M operator-() const { return M() - *this; }
    M operator+(const M& r) const { return M().set_v(v + r.v); }
    M operator-(const M& r) const { return M().set_v(v + MD - r.v); }
    M operator*(const M& r) const { return M().set_v(uint(ull(v) * r.v % MD)); }
    M operator/(const M& r) const { return *this * r.inv(); }
    M& operator+=(const M& r) { return *this = *this + r; }
    M& operator-=(const M& r) { return *this = *this - r; }
    M& operator*=(const M& r) { return *this = *this * r; }
    M& operator/=(const M& r) { return *this = *this / r; }
    bool operator==(const M& r) const { return v == r.v; }
    M pow(ll n) const {
        M x = *this, r = 1;
        while (n) {
            if (n & 1) r *= x;
            x *= x;
            n >>= 1;
        }
        return r;
    }
    M inv() const { return pow(MD - 2); }
    friend ostream& operator<<(ostream& os, const M& r) { return os << r.v; }
};
using Mint = ModInt<1000000007>;

Mint f[5010][2];
Mint dp[5010][2];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll N, A, B;
    cin >> N >> A >> B;
    if (A > B) {
        swap(A, B);
    }
    Mint ans = 0;
    if (B >= 2) {
        f[0][0] = 1;
        f[0][1] = 1;
        REP(i, 1, N + 1) {
            REP(k, 0, 2) {
                REP(j, 1, i + 1) {
                    if (k == 0 && j < A) {
                        continue;
                    }
                    f[i][k] += f[i - j][k ^ 1];
                }
            }
        }
        V<Mint> g(N + 1);
        g[0] = 1;
        REP(i, 1, N + 1) {
            g[i] = f[i][0] + f[i][1];
        }

        REP(i, 1, N) {
            if (i < A) {
                dp[i][0] += 1;
            }
            REP(j, 1, min(i, A)) {
                dp[i][0] += dp[i - j][1];
            }
            if (i < B) {
                dp[i][1] += g[i - 1];
            }
            REP(j, 1, min(i, B)) {
                Mint w = (j == 1)? 1: g[j - 2];
                dp[i][1] += dp[i - j][0] * w;
            }
            if (N - i < B) {
                ans += dp[i][0] * g[N - i - 1];
            }
            if (N - i < A) {
                ans += dp[i][1];
            }
        }
    }

    cout << Mint(2).pow(N) - ans << endl;
}


Measured memory_bytes: 3720