#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define endl "\n"
using namespace std;
using namespace __gnu_pbds;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T, typename key = less_equal<T>>
using ordered_set = tree<T, null_type, key, rb_tree_tag, tree_order_statistics_node_update>;
const ll mod = 1e6 + 7;
void solve()
{
ll n;
cin >> n;
ll a[n + 1];
for (ll i = 1; i <= n; i++) cin >> a[i];
int dp[2][n + 2][2];
for (ll i = 0; i < 2; i++)
for (ll j = 0; j <= n + 1; j++) dp[i][j][0] = dp[i][j][1] = 0;
dp[0][1][0] = 1;
for (ll i = 1; i <= n; i++)
{
for (ll j = 1; j <= n; j++) dp[i & 1][j][0] = dp[i & 1][j][1] = 0;
for (ll j = 1; j <= n; j++)
{
if (a[i] - j <= 1)
dp[i & 1][max(a[i], j)][0] += dp[(i - 1) & 1][j][0];
dp[i & 1][j][1] += min(j, a[i] - 1) * dp[(i - 1) & 1][j][0] % mod;
if (j + 1 < a[i])
dp[i & 1][j + 1][1] += dp[(i - 1) & 1][j][0];
dp[i & 1][j][1] += j * dp[(i - 1) & 1][j][1] % mod;
dp[i & 1][j + 1][1] += dp[(i - 1) & 1][j][1];
}
for (ll j = 1; j <= n; j++) dp[i & 1][j][0] %= mod, dp[i & 1][j][1] %= mod;
}
ll ans = 0;
for (ll i = 1; i <= n; i++) ans += dp[n & 1][i][1];
cout << (ans + 1) % mod << endl;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
ll t = 1;
// precomp();
// cin >> t;
for (ll cs = 1; cs <= t; cs++)
solve();
// cerr << "\nTime elapsed: " << clock() * 1000.0 / CLOCKS_PER_SEC << " ms\n";
}
