#include <bits/stdc++.h>
#define int long long
#define ll long long
#define pb push_back
#define fi first
#define se second
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
#define ld long double
using namespace std;
typedef pair<int,int> pii;
typedef pair<char,char> pcc;
typedef pair<int,pii> ipii;
typedef pair<pii,pii> ipiii;
const int MAXN = 1e3+20;
const int SQRT = 610;
const int MAXA = 50;
const int MOD = 1e6+7;
const int INF = 1e9+10;
const int LOG = 21;
const ld EPS = 1e-12;
int sum(int a, int b){ return (a+b)%MOD; }
int mul(int a, int b){ return (a*b)%MOD; }
void chsum(int &a, int b){ a = (a+b)%MOD; }
void chmul(int &a, int b){ a = (a*b)%MOD; }
int n, dp[MAXN][MAXN], a[MAXN];
signed main(){
// ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n;
for(int i=0; i<=n; i++) dp[0][i] = 1;
for(int i=1; i<=n; i++){
for(int j=1; j<=n; j++){
dp[i][j] = sum(mul(j-1, dp[i-1][j]), dp[i-1][j+1]);
}
}
int ans = 1, mx = 1;
for(int i=1; i<=n; i++) cin >> a[i];
for(int i=2; i<=n; i++){
if(a[i]==1) continue;
chsum(ans, mul(a[i]-2, dp[n-i][mx]) );
chsum(ans, dp[n-i][max(mx,a[i])] );
mx = max(mx, a[i]);
}
cout << ans << '\n';
}
