#define _CRT_SECURE_NO_WARNINGS
#pragma target("avx")
#pragma optimize("O3")
#pragma optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i,n) for(int i=0;i<(lint)(n);i++)
#define REP(i,n) for(int i=1;i<=(lint)(n);i++)
#define all(V) V.begin(),V.end()
#define lint long long
typedef std::pair<lint, lint> P;
constexpr int INF = INT_MAX/2;
constexpr lint LINF = LLONG_MAX/2;
constexpr double eps = DBL_EPSILON;
constexpr double PI=3.141592653589793238462643383279;
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
inline lint gcd(lint a, lint b) {
	while (b) {
		lint c = a;
		a = b; b = c % b;
	}
	return a;
}
inline lint lcm(lint a, lint b) {
	return a / gcd(a, b) * b;
}
bool isprime(lint n) {
	if (n == 1)return false;
	for (int i = 2; i * i <= n; i++) {
		if (n % i == 0)return false;
	}
	return true;
}
template<typename T>
T mypow(T a, unsigned int b) {
	if (!b)return T(1);
	if (b & 1)return mypow(a, b - 1) * a;
	T memo = mypow(a, b >> 1);
	return memo * memo;
}
lint modpow(lint a, lint b, lint m) {
	if (!b)return 1;
	if (b & 1)return modpow(a, b - 1, m) * a % m;
	lint memo = modpow(a, b >> 1, m);
	return memo * memo % m;
}
template<typename T>
void printArray(std::vector<T>& vec) {
	rep(i, vec.size() - 1)std::cout << vec[i] << " ";
	std::cout << vec.back() << std::endl;
}
template<typename T>
void printArray(T l, T r) {
	T rprev = r;
	rprev--;
	for (T i = l; i != rprev; i++) {
		std::cout << *i << " ";
	}
	std::cout << *rprev << std::endl;
}
template<unsigned int modulo = 1000000007>
class ModInt {
	lint value;
public:
	ModInt() : value(0) {}
	template<typename T>
	ModInt(T value = 0) : value(value) {
		if (value < 0)value = -(lint)(-value % modulo) + modulo;
		this->value = value % modulo;
	}
	inline operator int()const { return value; }
	inline ModInt& operator+=(const ModInt& x) {
		value += x.value;
		if (value >= modulo)value -= modulo;
		return *this;
	}
	inline ModInt& operator++() {
		if (value == modulo - 1)value = 0;
		else value++;
		return *this;
	}
	inline ModInt operator-()const {
		return ModInt(0) -= *this;
	}
	inline ModInt& operator-=(const ModInt& x) {
		value -= x.value;
		if (value < 0)value += modulo;
		return *this;
	}
	inline ModInt& operator--() {
		if (value == 0)value = modulo - 1;
		else value--;
		return *this;
	}
	inline ModInt& operator*=(const ModInt& x) {
		value = value * x.value % modulo;
		return *this;
	}
	inline ModInt& operator/=(ModInt rhs) {
		int exp = modulo - 2;
		while (exp) {
			if (exp & 1)*this *= rhs;
			rhs *= rhs;
			exp >>= 1;
		}
		return *this;
	}
	template<typename T> ModInt operator+(const T& rhs)const { return ModInt(*this) += rhs; }
	template<typename T> ModInt& operator+=(const T& rhs) { return operator+=(ModInt(rhs)); }
	template<typename T> ModInt operator-(const T& rhs)const { return ModInt(*this) -= rhs; }
	template<typename T> ModInt& operator-=(const T& rhs) { return operator-=(ModInt(rhs)); }
	template<typename T> ModInt operator*(const T& rhs)const { return ModInt(*this) *= rhs; }
	template<typename T> ModInt& operator*=(const T& rhs) { return operator*=(ModInt(rhs)); }
	template<typename T> ModInt operator/(const T& rhs)const { return ModInt(*this) /= rhs; }
	template<typename T> ModInt& operator/=(const T& rhs) { return operator/=(ModInt(rhs)); }
};
template<unsigned int T>
std::istream& operator>>(std::istream& ist, ModInt<T>& x) {
	lint a;
	ist >> a;
	x = a;
	return ist;
}
int n,a,b;
ModInt<> dp[5010][5010][2][2],sum[5010];
int main(){
	std::cin>>n>>a>>b;
	if(a<b)std::swap(a,b);
	ModInt<> ans=0;
	dp[0][0][0][0]=1;
	rep(i,n){
		sum[i]=sum[i-1];
		if(i-b<0)dp[i][0][1][0]+=sum[i-1];
		else dp[i][0][1][0]+=sum[i-1]-sum[i-b];
		rep(j,std::min(a,i+1)){
			rep(k,2){
				rep(l,2){
					if(k!=1&&l!=1)sum[i]+=dp[i][j][k][l];
					if(j+1<a)dp[i+1][j+1][0][0]+=dp[i][j][k][l];
					else ans+=dp[i][j][k][l]*mypow(ModInt<>(2),n-i-1);
					if(l){
						if(j+1<a)dp[i+1][j+1][0][1]+=dp[i][j][k][l];
						else ans+=dp[i][j][k][l]*mypow(ModInt<>(2),n-i-1);
					}
					if(i+b<=n&&!k&&!l){
						if(j+b<a)dp[i+b][j+b][0][1]+=dp[i][j][k][l];
						else ans+=dp[i][j][k][l]*mypow(ModInt<>(2),n-(i+b));
					}
				}
			}
		}
	}
	std::cout<<ans<<std::endl;
	return 0;
}

Measured memory_bytes: 788048