#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define all(a) a.begin(),a.end()
#define pb emplace_back
#define eb emplace_back
#define lb(v,k) (lower_bound(all(v),k)-v.begin())
#define ub(v,k) (upper_bound(all(v),k)-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define dupli(a) a.erase(unique(all(a)),a.end())
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
typedef multiset<ll> S;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=1000000007;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void noyes(T b){if(b)out("no");else out("yes");}
template<class T> void NoYes(T b){if(b)out("No");else out("Yes");}
template<class T> void NOYES(T b){if(b)out("NO");else out("YES");}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}

int main(){
    ll n,a,b;cin>>n>>a>>b;
    if(a==1||b==1)dame(modpow(2,n));
    if(a>b)swap(a,b);
    vi v(n+1);
    v[1]=1;
    REP(i,2,b){
        v[i]=v[i-1];
        for(int j=i-a-1;j>=1;j--)v[i]=(v[j]+v[i])%mod;
    }
    vi dp(n+1);
    dp[0]=1;
    REP(i,1,n+1){
        dp[i]=dp[i-1];
        if(i<a)dp[i]++;
        REP(j,1,b){
            if(j>=i)break;
            if(i!=n){
                ll k=dp[i-1-j];
                if(i-a-j>=0)k-=dp[i-a-j];
                dp[i]+=v[j]*(k+mod)%mod;
                k=min(i,b)-j-1-max(i-j-a+1,a)+1;
                if(k>0)dp[i]+=v[j]*k%mod;
                dp[i]%=mod;
            }
            if(i==n){
                ll k=dp[i-j];
                if(i-a-j>=0)k-=dp[i-a-j];
                dp[i]+=v[j]*(k+mod)%mod;
                if(i-a-j>i-b){
                    k=dp[i-a-j]-dp[i-b];
                    dp[i]+=v[j]*k%mod;
                }
                k=min(b-j-1,i-j)-max(i-j-a+1,a)+1;
                if(k>0)dp[i]+=v[j]*k;
                dp[i]%=mod;
            }
        }
    }
    out((modpow(2,n)-(dp[n]-dp[n-1])+mod)%mod);
}

Measured memory_bytes: 3700