#include <bits/stdc++.h>
#define MP make_pair
#define PB push_back
#define int long long
#define st first
#define nd second
#define rd third
#define FOR(i, a, b) for(int i =(a); i <=(b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REP(i, n) for(int i = 0;i <(n); ++i)
#define VAR(v, i) __typeof(i) v=(i)
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define __builtin_ctz __builtin_ctzll
#define __builtin_clz __builtin_clzll
#define __builtin_popcount __builtin_popcountll
using namespace std;
template<typename TH> void _dbg(const char* sdbg, TH h) { cerr<<sdbg<<"="<<h<<"\n"; }
template<typename TH, typename... TA> void _dbg(const char* sdbg, TH h, TA... t) {
  while(*sdbg != ',') { cerr<<*sdbg++; } cerr<<"="<<h<<","; _dbg(sdbg+1, t...);
}
#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define debugv(x) {{cerr <<#x <<" = "; FORE(itt, (x)) cerr <<*itt <<", "; cerr <<"\n"; }}
#else
#define debug(...) (__VA_ARGS__)
#define debugv(x)
#define cerr if(0)cout
#endif
#define next ____next
#define prev ____prev
#define left ____left
#define hash ____hash
typedef long long ll;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<pair<int, int> > VPII;
typedef vector<pair<ll, ll> > VPLL;

template<class C> void mini(C&a4, C b4){a4=min(a4, b4); }
template<class C> void maxi(C&a4, C b4){a4=max(a4, b4); }
template<class T1, class T2>
ostream& operator<< (ostream &out, pair<T1, T2> pair) { return out << "(" << pair.first << ", " << pair.second << ")";}
template<class A, class B, class C> struct Triple { A first; B second; C third;
  bool operator<(const Triple& t) const { if (st != t.st) return st < t.st; if (nd != t.nd) return nd < t.nd; return rd < t.rd; } };
template<class T> void ResizeVec(T&, vector<int>) {}
template<class T> void ResizeVec(vector<T>& vec, vector<int> sz) {
  vec.resize(sz[0]); sz.erase(sz.begin()); if (sz.empty()) { return; }
  for (T& v : vec) { ResizeVec(v, sz); }
}
typedef Triple<int, int, int> TIII;
template<class A, class B, class C>
ostream& operator<< (ostream &out, Triple<A, B, C> t) { return out << "(" << t.st << ", " << t.nd << ", " << t.rd << ")"; }
template<class T> ostream& operator<<(ostream& out, vector<T> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }
template<class T> ostream& operator<<(ostream& out, set<T> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }
template<class L, class R> ostream& operator<<(ostream& out, map<L, R> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }

const int P = 1e9 + 7;
const int N = 5e3 + 5;
int dp[N][N];
int pref[N][N];
int all[N];
int kon1[N];
int32_t main() {

  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(10);
  cin.tie(0);
  //double beg_clock = 1.0 * clock() / CLOCKS_PER_SEC;
  
  int n, a, b;
  cin>>n>>a>>b;
  if (a > b) {
    swap(a, b);
  }
  // mamy a < b
  // po zastiapeniu ciagow >=a zer jedynkami ma byc ciag b jedynek
  // dp[i][len] - liczba takich ciagow ze najdluzszy sufiks jedynek po zastapieniu ciagow a zer jedynkami ma dlugosc len
  
  //VVI dp(n + 2, VI(n + 2));
  dp[0][0] = 1;
  pref[0][0] = 1;
  all[0] = 1;
  kon1[0] = 1;
  RE (i, n) {
    REP (len, min(b, i + 1)) {
      if (len) {
        dp[i][len] = dp[i - 1][len - 1]; // dokladam 1
        kon1[i] = (kon1[i] + dp[i][len]) % P;
        pref[i - len][i] = (pref[i - len][i - 1] + dp[i][len]) % P;
      } else {
        dp[i][0] = dp[i - 1][0]; // dokladam 0 po zerze
        if (i >= 2) {
          dp[i][0] = (dp[i][0] + kon1[i - 1] + P) % P;
        }
        if (i >= a) {
          dp[i][0] = (dp[i][0] - kon1[i - a] + P) % P;
        }
      }
      // dp[i][len] += dp[i - x][len - x]  po x >= a gdzie koncza sie 1
      if (i >= a) {
        dp[i][len] = (dp[i][len] + pref[i - len][i - a]) % P; // dokladam 0
      }
      
      all[i] = (all[i] + dp[i][len]) % P;
      debug(i, len, dp[i][len]);
    }
  }
  int res = 1;
  RE (i, n) {
    res = 2 * res % P;
  }
  if (a == 1) {
    cout<<res<<endl;
    return 0;
  }
  REP (len, n) {
    res = (res - dp[n][len] + P) % P;
  }
  cout<<res<<endl;
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  return 0;
}


Measured memory_bytes: 237000