#include <bits/stdc++.h>
#include <ext/rope>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#define int long long
#define pb push_back
#define x first
#define y second
#define mk(a,b) make_pair(a,b)
#define rr return 0
#define sqr(a) ((a)*(a))
#define all(a) (a).begin(), (a).end()
#define sz(a) (int)(a).size()

using namespace std;
using namespace __gnu_cxx;
using namespace __gnu_pbds;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

template<class value, class cmp = less<value> >
using ordered_set = tree<value, null_type, cmp, rb_tree_tag, tree_order_statistics_node_update>;
template<class value, class cmp = less_equal<value> >
using ordered_multiset = tree<value, null_type, cmp, rb_tree_tag, tree_order_statistics_node_update>;
template<class key, class value, class cmp = less<key> >
using ordered_map = tree<key, value, cmp, rb_tree_tag, tree_order_statistics_node_update>;

/// find_by_order()
/// order_of_key()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int randll(int l = INT_MIN, int r = INT_MAX) {
    return uniform_int_distribution<int>(l, r)(rng);
}
const int INF = 1e9, MOD = 1e9 + 7; /// think
const ll LINF = 1e18;


const int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
inline bool inside (int x, int y, int n, int m) {
    return 0 <= x && 0 <= y && x < n && y < m;
}

template<class T> bool umin (T &a, T b) {return a > b ? (a = b, true) : false; }
template<class T> bool umax (T &a, T b) {return a < b ? (a = b, true) : false; }

inline int mul (int a, int b, int m = MOD) {
    return ((ll)a * b) % m;
}

inline int binpow (int a, int n, int m = MOD) {
    int ans = 1;
    for (; n; n >>= 1) {
        if (n & 1) ans = mul(ans, a, m);
        a = mul(a, a, m);
    }
    return ans;
}

inline void add (int &a, int x, int m = MOD) {
    a += x;
    if (a >= m) a -= m;
    if (a < 0) a += m;
}

inline int sum (int a, int b, int m = MOD) {
    a += b;
    if (a >= m) a -= m;
    if (a < 0) a += m;
    return a;
}

inline int inv (int x, int m = MOD) {
    return binpow(x, m - 2, m); /// only if m is prime
}

int n, a, b;
const int N = 5001;
int dp[N][N][2][2] = {}, pref[N][2] = {};
int pr[N][N][2][2] = {};

main()
{
    ios::sync_with_stdio(0);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n >> a >> b;
    if (a > b) swap(a, b);
    dp[0][0][0][1] = 1;
    dp[0][0][0][0] = 1;
    pr[0][0][0][0] = 1;
    pr[0][0][0][1] = 1;
    pref[0][0] = 1;
    for (int i = 1; i <= n; i++) {
        for (int t1 = 0; t1 < 2; t1++) {
            pref[i][t1] = pref[i - 1][t1];
            add(dp[i][0][t1][0], pref[i - 1][t1]);
            if (i - a >= 0) {
                add(dp[i][0][t1][0], -pref[i - a][t1]);
            }
        }
        for (int j = 0; j <= i; j++) {
            if (j) {
                add(dp[i][j][1][1], pr[i - 1][j - 1][1][0]);
            }
            int mnk = max(1, j - b + 1);
            if (i >= mnk && j >= mnk) {
                add(dp[i][j][j >= b][1], pr[i - mnk][j - mnk][0][0]);
            }
            if (i >= a && j >= a) {
                add(dp[i][j][1][0], pr[i - a][j - a][1][1]);
            }
            mnk = max(a, j - b + 1);
            if (i >= mnk && j >= mnk) {
                add(dp[i][j][j >= b][0], pr[i - mnk][j - mnk][0][1]);
            }
        }
        for (int j = 0; j <= i; j++) {
            for (int t1 = 0; t1 < 2; t1++) {
                add(pref[i][t1], dp[i][j][t1][1]);
                for (int t2 = 0; t2 < 2; t2++) {
                    if (j) {
                        pr[i][j][t1][t2] = pr[i - 1][j - 1][t1][t2];
                    }
                    add(pr[i][j][t1][t2], dp[i][j][t1][t2]);
                }
            }
        }
    }
    int ans = 0;
    for (int j = 0; j <= n; j++) {
        add(ans, dp[n][j][1][0]);
        add(ans, dp[n][j][1][1]);
    }
    cout << ans << '\n';
}


Measured memory_bytes: 433460