#include <bits/stdc++.h>
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")
#define rep(i,l,r) for (int i = l; i < r; i++)
#define repr(i,r,l) for (int i = r; i >= l; i--)
#define X first
#define Y second
#define pb push_back
#define endl '\n'
#define debug(x) cerr << #x << " : " << x << endl;
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pll;
constexpr int N = 1e4+20,mod = 1e6+7,inf = 1e9+10;
inline int mkay(int a,int b){
if (a+b >= mod) return a+b-mod;
if (a+b < 0) return a+b+mod;
return a+b;
}
inline int poww(int a,int k){
if (k < 0) return 0;
int z = 1;
while (k){
if (k&1) z = 1ll*z*a%mod;
a = 1ll*a*a%mod;
k >>= 1;
}
return z;
}
int a[N],mx[N];
int dp[2][N],n;
int main(){
ios :: sync_with_stdio(0); cin.tie(0);
cin >> n;
rep(i,1,n+1){
cin >> a[i];
mx[i] = max(mx[i-1],a[i]);
}
int ans = 1;
bool f = (n&1);
f = 1-f;
rep(j,0,n+1){
dp[f][j] = 1;
}
repr(i,n,1){
int d = (i&1);
int g = 1ll*(a[i]-1)*dp[1-d][mx[i-1]]%mod;
ans = mkay(ans,g);
rep(j,0,i+1){
dp[d][j] = mkay(dp[1-d][j+1],1ll*dp[1-d][j]*j%mod);
}
}
cout << ans;
}
