//雪花飄飄北風嘯嘯
//天地一片蒼茫
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define ll long long
#define ii pair<ll,ll>
#define iii pair<ii,ll>
#define fi first
#define se second
#define endl '\n'
#define debug(x) cout << #x << " is " << x << endl;
#define rep(x,start,end) for(auto x=(start)-((start)>(end));x!=(end)-((start)>(end));((start)<(end)?x++:x--))
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()
ll MAX(ll a){return a;}
ll MIN(ll a){return a;}
template<typename... Args>
ll MAX(ll a,Args... args){return max(a,MAX(args...));}
template<typename... Args>
ll MIN(ll a,Args... args){return min(a,MIN(args...));}
#define indexed_set tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
const int MOD=1000007;
int n;
int arr[1005];
ll memo[1005][1005];
ll dp(int i,int j){
if (i==n-1) return 1;
if (memo[i][j]!=-1) return memo[i][j];
return memo[i][j]=(dp(i+1,j+1)+dp(i+1,j)*j)%MOD;
}
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
memset(memo,-1,sizeof(memo));
cin>>n;
rep(x,0,n) cin>>arr[x];
ll ans=1;
int mx=0;
rep(x,0,n){
ans=(ans+dp(x,mx)*(arr[x]-1));
mx=max(mx,arr[x]);
}
cout<<ans<<endl;
}
