#include <bits/stdc++.h>
#define int long long
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
using namespace std;
const int MOD=1e9+7;
signed main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr);
int n; cin >> n;
vector<vector<int>> dp(n,vector<int>(n,0));
dp[0][0]=1;
for (int i = 1; i < n; i++)
{
for (int j = 0; j < n; j++)
{
dp[i][j]=(dp[i-1][j]*(j+1))%MOD;
if(j>0) dp[i][j]=(dp[i][j]+dp[i-1][j-1])%MOD;
}
}
vector<int> a(n);
for (int i = 0; i < n; i++) cin >> a[i];
int mx=1;
int sm=1;
for (int i = 1; i < n-1; i++) {
int nsm=0;
for (int j = 0; j < n; j++)
{
nsm=(nsm+dp[(n-i)-2][j])%MOD;
}
nsm=(nsm*(a[i]-1))%MOD;
nsm=(nsm*(mx+1))%MOD;
if(a[i]==1) continue;
mx=max(a[i],mx);
sm=(sm+(nsm%MOD))%MOD;
}
sm=(sm+a[n-1]-1)%MOD;
cout << sm << "\n";
return 0;
}
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