#include <bits/stdc++.h>
using namespace std;
#define rep(i , j , k) for (int i = j; i < (int)k; i++)
#define pb push_back
#define mt make_tuple
#define all(x) x.begin(),x.end()
typedef long long ll;
typedef pair<int , int> pii;
typedef pair<ll, ll> pll;
typedef long double ld;
typedef complex<ld> point;
typedef pair<ld , ld> pld;
typedef vector<pld> vi;
inline void fileIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
template<class T , class S>
inline bool smin(T &a, S b) { return (T)b < a ? a = b , 1 : 0; }
template<class T , class S>
inline bool smax(T &a, S b) { return a < (T)b ? a = b , 1 : 0; }
constexpr int N = 1e4 + 10;
constexpr int MOD = 1e6 + 7;
template<typename T>
inline T mod(T &v) { return v = (v % MOD + MOD) % MOD; }
template<typename S, typename T>
inline S add(S &l, T r) { return mod(l += r); }
ll dp[2][N]; // dp i , j => i nafar ke ghable avlin nafar j t ahalat dashtim
// dp[i][j] = j * dp[i - 1][j] + dp[i - 1][j + 1];
int a[N], b[N], n;
int main() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#ifndef LOCAL
//fileIO("superposition");
#endif
cin >> n;
rep(i , 0 , n) {
cin >> a[i];
b[i + 1] = max(a[i] , b[i]);
}
rep(i , 0 , n + 2)
dp[0][i] = 1;
ll res = 0;
rep(i , 1 , n + 1) {
int id = i & 1;
memset(dp[id] , 0 , sizeof(dp[0]));
add(res , (a[n - i] - 1) * dp[id ^ 1][b[n - i]]);
rep(j , 0 , n + 1)
add(dp[id][j] , j * dp[id ^ 1][j] + dp[id ^ 1][j + 1]);
}
cout << res + 1 << endl;
return 0;
}
