#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 = 1e4+10;
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 (1ll*a*b)%MOD; }
void chsum(int &a, int b){ a = (a+b)%MOD; }
void chmul(int &a, int b){ a = (1ll*a*b)%MOD; }
int n, dp[3][MAXN], a[MAXN];
int mx[MAXN];
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n;
// cout<<dp[2][2]<< ' '<<dp[1][3]<<" pp\n";
int ans = 1;
for(int i=1; i<=n; i++) cin >> a[i];
for(int i=1; i<=n; i++) mx[i] = max(mx[i-1],a[i]);
for(int i=0; i<=n; i++) dp[0][i] = 1;
for(int i=n; i>=2; i--){
for(int j=1; j<=a[i]-1; j++)
chsum(ans, dp[0][max(mx[i-1]+1, j+1)] );
for(int j=1; j<=n; j++){
dp[1][j] = sum(mul(j-1, dp[0][j]), dp[0][j+1]);
}
for(int j=1; j<=n; j++)
dp[0][j] = dp[1][j];
}
cout << ans << '\n';
}
