2018

#include <iostream>

using namespace std;

int const m = 1000000007;
long long mas[50000][2];

int main()
{
    int n, a, b;
    cin >> n >> a >> b;
    mas[0][0] = 1;
    mas[0][1] = 1;
    for (int i = 1; i < n; i++)
    {
        mas[i][0] = mas[i - 1][0] + mas[i - 1][1];
        if (i >= a)
            mas[i][0] -= mas[i - a][0];
        mas[i][0] = mas[i][0] % m;
        mas[i][1] = mas[i - 1][0] + mas[i - 1][1];
        if (i >= b)
            mas[i][1] -= mas[i - b][1];
        mas[i][1] = mas[i][1] % m;
    }
    cout << (mas[n - 1][0] + mas[n - 1][1]) % m;
}