#include <bits/stdc++.h>
using namespace std;
#define int long long
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1e6 + 7;
void Solve() {
int n;
cin >> n;
int a[n + 1], mx[n + 1];
mx[0] = 0;
for(int i = 1; i <= n; i++) {
cin >> a[i];
mx[i] = max(mx[i - 1], a[i]);
}
int dp[2][n + 5];
for(int i = 0; i <= n + 4; i++) {
dp[0][i] = 1;
}
int ans = 1;
for(int i = n - 1; i > 0; i--) {
int cur = (n - i) % 2, prev = 1 - cur;
for(int j = 1; j <= n; j++) {
int x = (dp[prev][j] * j) % MOD;
x += dp[prev][j + 1];
x %= MOD;
dp[cur][j] = x;
}
for(int j = a[i] - 1; j > 0; j--) {
int temp = max(mx[i - 1], j);
ans += dp[cur][temp];
ans %= MOD;
}
}
cout << (ans + a[n] - 1) % MOD << "\n";
}
int32_t main() {
auto begin = std::chrono::high_resolution_clock::now();
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
//cin >> t;
while(t--) {
Solve();
}
auto end = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n";
return 0;
}
