#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<array>
#include<map>
#include<iomanip>
#include<assert.h>
#include<list>
#include<bitset>
#include<stack>
#include<memory>
#include<numeric>
using namespace std;
using namespace std::chrono;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define REP(i, n) for(int i = 0;i < (n);i++)
/*cout<<fixed<<setprecision(20);cin.tie(0);ios::sync_with_stdio(false);*/
const llint mod=1000000007;
const llint inf=2.19e15+1;
const long double pai=3.141592653589793238462643383279502884197;
const long double eps=1e-10;
template <class T,class U>bool chmin(T& a,U b){if(a>b){a=b;return true;}return false;}
template <class T,class U>bool chmax(T& a,U b){if(a<b){a=b;return true;}return false;}
llint gcd(llint a,llint b){if(a%b==0){return b;}else return gcd(b,a%b);}
llint lcm(llint a,llint b){if(a==0){return b;}return a/gcd(a,b)*b;}
template<class T> void SO(T& ve){sort(ve.begin(),ve.end());}
template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());}
template<class T>llint LBI(const vector<T>&ar,T in){return lower_bound(ar.begin(),ar.end(),in)-ar.begin();}
template<class T>llint UBI(const vector<T>&ar,T in){return upper_bound(ar.begin(),ar.end(),in)-ar.begin();}

#include <algorithm>
#include <utility>
#include <type_traits>
#include <cstdint>
//永夜作
#define mnt mint_base
class mint_base;
//mint_base_base型用の累乗関数
constexpr mint_base m_pow(mint_base x, uint64_t n)noexcept;
//mod計算を自動で行う整数テンプレートクラス
class mint_base
{
public:
	constexpr mint_base operator+(const mint_base &other)const noexcept
	{auto v = *this;return v += other;}
	constexpr mint_base operator-(const mint_base &other)const noexcept
	{auto v = *this;return v -= other;}
	constexpr mint_base operator*(const mint_base &other)const noexcept
	{auto v = *this;return v *= other;}
	constexpr auto operator/(const mint_base &other)const noexcept
	{auto v = *this;return v /= other;}
	constexpr mint_base & operator+=(const mint_base &other) noexcept
	{a += other.a;if (mod <= a) { a -= mod; };return *this;}
	constexpr mint_base & operator-=(const mint_base &other) noexcept
	{if (a >= other.a) {a -= other.a;}else {a = (a + mod) - other.a;}return *this;}
	constexpr mint_base & operator*=(const mint_base &other) noexcept
	{a *= other.a;a %= mod;return *this;}
	constexpr mint_base & operator/=(const mint_base &other) noexcept
	{return *this *= ~other;}
	constexpr mint_base operator+()const noexcept { return *this; }
	constexpr mint_base operator-()const noexcept
	{return{ mod - a, mod_value_tag{} };}
	constexpr mint_base & operator++() noexcept
	{if (mod <= ++a) { a = 0; };return *this;}
	constexpr mint_base & operator--() noexcept
	{if (a <= 0) { a = mod; };--a;return *this;}
	constexpr mint_base operator++(int) noexcept
	{auto tmp = *this;++*this;return tmp;}
	constexpr mint_base operator--(int) noexcept
	{auto tmp = *this;--*this;return tmp;}
	constexpr mint_base operator~()const noexcept
	{return m_pow(*this, mod-2);}
	constexpr mint_base & operator=(const mint_base &other) noexcept
	{a=other.a;return *this;}
	constexpr explicit operator uint64_t()const noexcept
	{return a;}
	constexpr explicit operator int()const noexcept
	{return a;}
	constexpr explicit operator unsigned()const noexcept
	{return (unsigned)a;}
	static constexpr uint64_t getmod() noexcept
	{return mod;}
	constexpr mint_base(uint64_t a_) noexcept :a(a_ % mod) {}
	constexpr mint_base()noexcept : a(0) {}
	struct mod_value_tag {};
	constexpr mint_base(uint64_t a_, mod_value_tag) :a(a_) {}
private:
	uint64_t a;
};

//mint_base型用の累乗関数
constexpr mint_base m_pow(mint_base x,uint64_t n)noexcept
{
	mint_base res = 1;
	while(n>0){
		if(n&1){res*=x;}
		x*=x;
		n>>=1;
	}
	return res;
}
//mint_baseの階乗計算
//0からxまでの階乗を返す
//O(x)時間が必要
vector<mint_base> fla;//階乗が入る
void fla_set(mint_base x)
{
	fla.resize(((uint64_t)x)+1);
	fla[0] = 1;
	for (uint64_t i = 1; i <= (uint64_t)x;i++){fla[i]=fla[i-1]*i;}
}
vector<mint_base> gya;//~fla[i] が入る

//O(x+log mod)で求める O(xlogmod)より速い
void fla_gya_set(mint_base x)
{
	fla_set(x);
	gya.resize(((uint64_t)x)+1);
	gya[(uint64_t)x]=~fla[(uint64_t)x];
	for(uint64_t i =(uint64_t)x;i>0;i--){gya[i-1]=gya[i]*i;}
}

//mint_base型のstreamへの出力
std::ostream& operator<<(std::ostream& os, mint_base i)
{os<<(uint64_t)i;return os;}
//mint_base型のstreamからの入力
std::istream& operator >> (std::istream& is, mint_base& i)
{uint64_t tmp;is>>tmp;i=tmp;return is;}

int main(void){
	int i,j,k,n,A,B;cin>>n>>A>>B;
	if(A>B){swap(A,B);}
	
	//できない数をカウントする
	
	
	
	static mint_base dp[5015][5015]={};
	static mint_base ep[5015][5015]={};
	mint_base wa[5015]={};
	mint_base ans=0;
	dp[0][0]=1;
	for(i=0;i<=n;i++){
		mint_base aaa=0;
		wa[i+1]+=wa[i];
		dp[i][1]+=wa[i];
		for(j=0;j<B;j++){
			
			dp[i][j]+=ep[i][j];
			//cout<<dp[i][j]<<" ";
			ep[i+1][j+1]+=ep[i][j];
			dp[i+1][j+1]+=dp[i][j];//1
			if(i>0&&j==0){continue;}
			aaa+=dp[i][j];
			if(i+A+1<=n+5&&j+A+1<=n+5){ep[i+A+1][j+A+1]+=dp[i][j];}
		}
		//cout<<endl;
		//cout<<aaa<<endl;
		wa[i+2]+=aaa;
		if(i+A+1<=n+5){wa[i+A+1]-=aaa;}
		
	}
	for(i=0;i<=n;i++){
		for(j=0;j<B;j++){
			if(n-i+j<B||n-i<A){ans+=dp[i][j];}
		}
	}
	mint_base eee=1;
	for(i=0;i<n;i++){eee*=2;}
	cout<<eee-ans<<endl;
	return 0;
}


Measured memory_bytes: 395180