#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define SZ(x) ((int)((x).size()))

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
    bool done_something = false;
    stringstream res;
    res << "[";
    for (; begin_iter != end_iter and counter; ++begin_iter) {
        done_something = true;
        counter--;
        res << *begin_iter << ", ";
    }
    string str = res.str();
    if (done_something) {
        str.pop_back();
        str.pop_back();
    }
    str += "]";
    return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
    vector<int> ord(size);
    for (int i = 0; i < size; i++) ord[i] = i;
    sort(ord.begin(), ord.end(), compare);
    return ord;
}

template <typename T>
bool MinPlace(T& a, const T& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T>
bool MaxPlace(T& a, const T& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename S, typename T>
ostream& operator <<(ostream& out, const pair<S, T>& p) {
    out << "{" << p.first << ", " << p.second << "}";
    return out;
}

template <typename T>
ostream& operator <<(ostream& out, const vector<T>& v) {
    out << "[";
    for (int i = 0; i < (int)v.size(); i++) {
        out << v[i];
        if (i != (int)v.size()-1) out << ", ";
    }
    out << "]";
    return out;
}

template<class TH>
void _dbg(const char* name, TH val){
    clog << name << ": " << val << endl;
}
template<class TH, class... TA>
void _dbg(const char* names, TH curr_val, TA... vals) {
    while(*names != ',') clog << *names++;
    clog << ": " << curr_val << ", ";
    _dbg(names+1, vals...);
}

#if DEBUG && !ONLINE_JUDGE
    ifstream input_from_file("input.txt");
    #define cin input_from_file

    #define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
    #define dbg_arr(x, len) clog << #x << ": " << print_iterable(x, x+len, -1) << endl;
#else
    #define dbg(...)
    #define dbg_arr(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

const int MAXN = 5010;
LL f[MAXN][MAXN];
LL pot[MAXN];
const LL mod = 1e9 + 7;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); // Remove in problems with online queries!

    pot[0] = 1;
    for (int i = 1; i < MAXN; i++) pot[i] = 2*pot[i-1] % mod;

    int N, A, B;
    cin >> N >> A >> B;
    if (A > B) swap(A, B);
    if (A == 1) {
        cout << pot[N] << "\n";
        return 0;
    }
    vector<LL> pref(MAXN, 0);
    vector<vector<LL>> hardpref(MAXN, vector<LL>(MAXN, 0));
    for (int n = 1; n <= N; n++) {
        for (int k = 0; k < B; k++) {
            f[n][k] += f[n-1][k+1];
            if (k == B-1) f[n][k] += pot[n-1];
            if (k + n >= B and n >= A) f[n][k]++;
            f[n][k] += pref[n-1] - ((n-A >= 0)?pref[n-A]:0);
            // n-1-A, 1+k+A
            // n-z, k+z
            int low = 1+A;
            int high = min(n, B-k-1);
            if (low <= high) {
                f[n][k] += hardpref[n-low][k+low];
                if (high != n) f[n][k] -= hardpref[n-high-1][k+high+1];
            }
            // for (int t = A; 1+t <= min(n, B-k-1); t++) {
                // f[n][k] += f[n-1-t][1+k+t];
            // }
            int z = max(B-k, A+1);
            if (n-z+1 >= 0) f[n][k] += pot[n-z+1]-1;
            f[n][k] %= mod;
            hardpref[n][k] = (hardpref[n-1][k+1] + f[n][k]) % mod;
        }
        pref[n+1] = (pref[n] + f[n][1]) % mod;
    }   
    // dbg(f[1][2]);
    if (f[N][0] < 0) f[N][0] += mod;
    cout << f[N][0] << "\n";
}


Measured memory_bytes: 395432