/** MIT License Copyright (c) 2018 Vasilyev Daniil **/
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
template<typename T> using v = vector<T>;
#define int long long
typedef string str;
typedef vector<int> vint;
#define rep(a, l, r) for(int a = (l); a < (r); a++)
#define pb push_back
#define sz(a) ((int) a.size())
const long long inf = 4611686018427387903; //2^62 - 1
#if 0 //FileIO
const string fileName = "";
ifstream fin ((fileName == "" ? "input.txt" : fileName + ".in" ));
ofstream fout((fileName == "" ? "output.txt" : fileName + ".out"));
#define get fin>>
#define put fout<<
#else
#define get cin>>
#define put cout<<
#endif
#define eol put endl
void read() {} template<typename Arg,typename... Args> void read (Arg& arg,Args&... args){get (arg) ;read(args...) ;}
void print(){} template<typename Arg,typename... Args> void print(Arg arg,Args... args){put (arg)<<" ";print(args...);}
void debug(){eol;} template<typename Arg,typename... Args> void debug(Arg arg,Args... args){put (arg)<<" ";debug(args...);}
int getInt(){int a; get a; return a;}
//code goes here
const int mod = 1e6 + 7;
void run() {
int n;
get n;
int ans = 1;
int lim = 0;
rep(i, 0, n) {
int a;
get a;
if (a == 1)
continue;
else {
int dp[n - i][n];
rep(j, 0, n - i)
rep(k, 0, n)
dp[j][k] = 0;
dp[0][lim] = a - 1;
rep(j, 1, n - i)
rep(k, 0, n) {
dp[j][k] = (dp[j][k] + (dp[j - 1][k] * (k + 1)) % mod) % mod;
if (k)
dp[j][k] = (dp[j][k] + dp[j - 1][k - 1]) % mod;
}
rep(j, 0, n)
ans = (ans + dp[n - i - 1][j]) % mod;
}
lim = max(lim, a - 1);
}
put ans;
}
int32_t main() {srand(time(0)); ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); put fixed; put setprecision(15); run(); return 0;}
