#include <bits/stdc++.h>
#ifdef ULVI
#define db(x) cerr<<"[ "<<#x<<" = "<<(x)<<" ]\n"
#define dbv(v) cerr<<#v<<" = [ ";for(auto &__x : v)cerr<<__x<<' ';cerr<<"]\n"
#define line() cerr<<string(80, '-')<<'\n'
#else
#define db(x)
#define dbv(v)
#define line()
#endif
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define ff first
#define ss second
#define enld endl
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<ll,ll> pll;
const ll sz=2e5+100;
const ll mod=1000007;
const ll inf=1e18;
template<class T>
using indexed_set=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
vector<ll> f(ll l,ll r,vector<ll> &v){
if(l>r) return {0};
ll ln=r-l+1;
vector<ll> res;
for(ll i=0;i<(1LL<<ln);i++){
ll sum=0;
for(ll j=0;j<ln;j++) if(i>>j&1) sum+=v[l+j];
res.push_back(sum);
}
return res;
}
void solve(){
ll n;
cin>>n;
vector<ll> v(n+5);
for(ll i=1;i<=n;i++) cin>>v[i];
vector<vector<ll>> dp(n+5,vector<ll>(n+5));
for(ll i=1;i<=n;i++) dp[0][i]=1;
for(ll i=1;i<=n;i++) for(ll j=n;j>=1;j--) dp[i][j]=(j*dp[i-1][j]+dp[i-1][j+1])%mod;
ll ans=1,mx=1;
for(ll i=2;i<=n;i++){
ans=(ans+min(v[i]-1,mx)*dp[n-i][mx])%mod;
mx=max(mx,v[i]);
}
cout<<ans<<'\n';
}
int main(){
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
ll t=1;
//cin>>t;
for(ll _=1;_<=t;_++){
//cout<<"Scenario #"<<_<<":\n";
solve();
}
}
