/*
#ifndef ONLINE_JUDGE
#include "AkbarKING.h" // aska geldi akbarking.h
#else
#define debug(...)
#define debugArr(...)
#define debugG(...)
#endif
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/hash_policy.hpp>
#define int long long
#define $AzH_TxdmN$ ios_base::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("fast-math")
#define ep emplace_back
#define pb push_back
#define pii pair<int,int>
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using __indexed_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
using __indexed_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int sz = 2e3+9;
const int LOG = 63;
const int MOD = 1e9+7;
const int INF = 1e18;
int a[sz],dp[sz][sz],sdp[sz];
int n;
void solve()
{
cin>>n;
for (int i = 0; i < n; ++i)
{
cin>>a[i];
}
sdp[0] = a[0];
for (int i = 1; i < n; ++i)
{
sdp[i] = max(sdp[i],sdp[i-1]);
}
for (int i = 0; i <= n; ++i)
{
for (int j = 0; j <= n; ++j)
{
dp[i][j] = 1;
}
}
int res = 1;
for (int i = n-1; i >= 1; --i)
{
if (i != n-1)
{
for (int j = 1; j <= i+1; ++j)
{
dp[i][j] = (((dp[i+1][j]*j))%MOD + (dp[i+1][j+1])%MOD)%MOD;
}
}
res = (res+dp[i][sdp[i-1]]*(a[i]-1))%MOD;
}
cout<<res<<'\n';
}
signed main()
{
$AzH_TxdmN$
int t = 1;
//cin>>t;
while (t--)
{
solve();
}
}
