#include<bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "
#pragma GCC optimize("Ofast")
#define int long long
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int range_rng(int l, int r)
{
return uniform_int_distribution<int>(l,r)(rng);
}
const int mod=1e6+7;
int dp[1005][1005][2];
int n;
vector<int> v;
void modit(int &x)
{
if (x>=mod)
x-=mod;
}
int smaller(vector<int> &v)///il fac strict (cred)
{
int i,j,ans;
dp[0][0][1]=1;
for (i=1;i<=n;i++)
{
for (j=1;j<=n;j++)
{
dp[i][j][0]+=(dp[i-1][j][0]*j)%mod;
modit(dp[i][j][0]);
dp[i][j][0]+=(dp[i-1][j-1][0]);
modit(dp[i][j][0]);
dp[i][j][0]+=(dp[i-1][j][1]*(v[i]-1))%mod;
modit(dp[i][j][0]);
if (v[i]<=j)
dp[i][j][1]+=(dp[i-1][j][1]);
if (v[i]==j)
dp[i][j][1]+=(dp[i-1][j-1][1]);
modit(dp[i][j][1]);
}
}
ans=0;
for(j=1;j<=n;j++)
{
ans+=dp[n][j][0];
modit(ans);
}
return ans;
}
signed main()
{
/*
ifstream fin("arbore.in");
ofstream fout("arbore.out");
*/
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int i,x;
cin >> n;
v.push_back(0);
for (i=1;i<=n;i++)
{
cin >> x;
v.push_back(x);
}
cout << (smaller(v)+1)%mod;
return 0;
}
