#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;
struct mi {
    int val;
    explicit operator int() const { return val; }
    mi() { val = 0; }
    mi(const ll& v) {
        val = (-MOD <= v && v <= MOD) ? v : v % MOD;
        if (val < 0) val += MOD; }
    friend ostream& operator<<(ostream& os, const mi& a) { return os << a.val; }
    friend bool operator==(const mi& a, const mi& b) { return a.val == b.val; }
    friend bool operator!=(const mi& a, const mi& b) { return !(a == b); }
    friend bool operator<(const mi& a, const mi& b) { return a.val < b.val; }
    mi operator-() const { return mi(-val); }
    mi& operator+=(const mi& m) {
        if ((val += m.val) >= MOD) val -= MOD;
        return *this; }
    mi& operator-=(const mi& m) {
        if ((val -= m.val) < 0) val += MOD;
        return *this; }
    mi& operator*=(const mi& m) { val = (long long) val*m.val%MOD;
        return *this; }
    friend mi pow(mi a, long long p) {
        mi ans = 1; assert(p >= 0);
        for (; p; p /= 2, a *= a) if (p&1) ans *= a;
        return ans; }
    friend mi inv(const mi& a) { assert(a != 0); return pow(a,MOD-2); }
    mi& operator/=(const mi& m) { return (*this) *= inv(m); }
    friend mi operator+(mi a, const mi& b) { return a += b; }
    friend mi operator-(mi a, const mi& b) { return a -= b; }
    friend mi operator*(mi a, const mi& b) { return a *= b; }
    friend mi operator/(mi a, const mi& b) { return a /= b; }
};
const int MAX = 5e3 + 5;
mi dp[MAX][MAX][2]; // have i placed a big 0 stuff
mi prefix[MAX][2*MAX][2]; // sum for up to i, difference is j, last is last
mi sum[MAX][2];
int a, b;
mi prefix_sum(int l, int r, int diff, int last){
    if(r < 0) return 0;
    if(l > r) return 0;
    if(l <= 0) return prefix[r][diff][last];
    return prefix[r][diff][last] - prefix[l - 1][diff][last];
}
mi sum_sum(int l, int r, int last){
    if(r < 0) return 0;
    if(l > r) return 0;
    if(l <= 0) return sum[r][last];
    return sum[r][last] - sum[l - 1][last];
}
int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int n; cin >> n >> a >> b;
    if(a<b) swap(a, b);
    sum[0][1] = 1;
    sum[0][0] = 1;
    prefix[0][MAX][0] = 1;
    prefix[0][MAX][1] = 1;
    for(int i = 1; i <= n; i++){
        for(int last = 0; last < 2; last++){
            sum[i][last] = sum[i - 1][last];
        }
        for(int j = 0; j < 2 * MAX; j++){
            for(int last = 0; last < 2; last++){
                prefix[i][j][last] = prefix[i - 1][j][last];
            }
        }
        for(int j = 0; j < a; j++){
            for(int last = 0; last < 2; last ++){
                if(last == 0){
                    dp[i][j][last] = prefix_sum(i - min(a - 1, j), i - 1, i - j + MAX, last ^ 1);
                }
                else{
                    if(j == 0){
                        dp[i][j][last] = sum_sum(i - b + 1, i - 1, last ^ 1);
                    }
                    else{
                        dp[i][j][last] = prefix_sum(i - min(a - 1, j), i - b, i - j + MAX, last ^ 1);
                    }
                }
                sum[i][last] += dp[i][j][last];
                prefix[i][i - j + MAX][last] += dp[i][j][last];
            }
        }
    }
    mi ans = 1;
    for(int i = 0; i < n; i++) ans *= 2;
    mi sub = 0;
    for(int j = 0; j < a; j++){
        for(int last = 0; last < 2; last++){
            sub += dp[n][j][last];
        }
    }
    ans -= sub;
    cout << ans.val << '\n';
}


Measured memory_bytes: 590808