abc178_d - Redistribution

using namespace std;
using ll = long long;
using ii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
int const MOD = 1e9 + 7;
int const SMAX = 2000 + 11;
ll mem[SMAX];
bool vis[SMAX];
ll add(ll a, ll b) { return ((a + MOD % MOD) + (b + MOD % MOD)) % MOD; }
ll dp(int s)
{
    if (s == 0)
        return 1;
    if (vis[s])
        return mem[s];
    ll &ans = mem[s];
    vis[s] = true;
    for (int d = 3; d <= s; ++d)
        ans = add(ans, dp(s - d));
    return ans;
}
int main(void)
{
    int s;
    cin >> s;
    cout << dp(s) << endl;
    return 0;
}