#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(); } }