#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);

void chmin(int &a, int b) {
	a = min(a, b);
}
void chmax(int &a, int b) {
	a = max(a, b);
}
ll mod_pow(ll a, ll n, ll m = mod) {
	a %= m;
	ll res = 1;
	while (n) {
		if (n & 1)res = res * a%m;
		a = a * a%m; n >>= 1;
	}
	return res;
}

struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n%mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint &a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint &a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint &a, modint b) { a.n = ((ll)a.n*b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, int n) {
	if (n == 0)return modint(1);
	modint res = (a*a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p%a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
const int max_n = 1 << 20;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}

int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };


modint dp[5002][5002][2];
modint rdp[5002][5002];
modint rdp2[5002][5002];
modint rdp3[5002];


void solve2(int n,int k) {
	rdp[1][1] = 2;
	rep1(i, n-1) {
		rep(j, k) {
			if (j + 1 < k) {
				rdp[i + 1][j + 1] += rdp[i][j];
			}
			rdp[i + 1][1] += rdp[i][j];
		}
	}
	modint ans = mod_pow(2, n);
	rep(j, k)ans -= rdp[n][j];
	cout << ans << "\n";
}
void solve() {
	int n, a, b; cin >> n >> a >> b;
	if (a == b) {
		solve2(n, a); return;
	}
	if (a > b)swap(a, b);
	dp[0][0][0] = dp[0][0][1] = 1;

	rdp3[1] = 1;
	rdp2[1][1] = 1;
	rdp[1][1] = 1;

	rep1(i, n) {
		rdp3[i + 1] = rdp3[i];
		rep(j, min(b,i+1)) {
			//cout << "?? " << i << " " << j << " " << rdp[i - j][b - j] << "\n";
			dp[i][j][0] = rdp[i][j];
			int l1 = i - a + 1;
			int l2 = j - a + 1;
			if (l2 < 0) {
				l1 += -l2; l2 = 0;
			}
			int s1 = i - b + 1;
			int s2 = j - b + 1;
			if (s2 < 0) {
				s1 += -s2; s2 = 0;
			}
			int ri = i;
			dp[i][j][1] = rdp2[l1][l2]-rdp2[s1][s2];
			if (j == 0) {
				int le = i - a + 1; if (le < 0)le = 0;
				dp[i][j][1] += rdp3[i] - rdp3[le];
			}

			rdp2[i + 1][j + 1] = rdp2[i][j]+dp[i][j][0];
			rdp[i+1][j + 1] = rdp[i][j]+dp[i][j][1];
			rdp3[i + 1] += dp[i][j][0];
		}
	}
	/*rep1(i, n) {
		rep(j, b) {
			rep(k, 2) {
				cout << i << " " << j << " " << k << " " << dp[i][j][k] << "\n";
			}
		}
	}*/
	modint ans = mod_pow(2,n);
	rep(j, b) {
		rep(k, 2) {
			ans -= dp[n][j][k];
		}
	}
	cout << ans << "\n";
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(7);
	//init_f();
	//init();
	solve();
	stop
		return 0;
}


Measured memory_bytes: 801912