#include <bits/stdc++.h> 
using namespace std; 
using ll=long long; 
  
#define all(a) a.begin(), a.end() 
  
int solve(); 
  
int main(){ 
    ios_base::sync_with_stdio(0);cin.tie(0); 
    int t=1; 
    //cin>>t; 
    while (t--) solve(); 
} 
const ll mod=1e9+7; 
const ll maxn=2001; 
  
//x^mod-2=1/x 
ll binpow(ll a,ll b){ 
    if (b==0) return 1; 
    ll res=binpow(a,b/2); 
    if (b%2) return res*res%mod*a%mod; 
    return res*res%mod; 
} 
vector<ll> a(maxn, 0); 
vector<ll> fact(maxn*maxn, 1); 
  
ll ncr(ll n, ll k){ 
    return fact[n]*binpow(fact[n-k]*fact[k]%mod, mod-2)%mod; 
} 
  
ll q(ll height, ll base , ll amount){
	if (height>=base) swap(height , base); //-- 
	ll res=ncr(base, amount)*fact[height]%mod*binpow(fact[height-amount], mod-2)%mod; 
    return res; 
}

ll spec(ll height, ll base){ 
    if (height>base) return 0LL; //-- 
    if (height<=0) return 1LL; 
    ll res=ncr(base, height)*fact[height]%mod; 
    return res; 
} 
  
  
int solve(){ 
    ll n; 
    cin>>n; 
    ll div=0; 
    for (ll i=1;i<=n;i++){ 
        cin>>a[i]; 
        if (a[i]!=a[i-1]) div=i; 
    } 
    for (ll i=2;i<fact.size();i++) fact[i]=fact[i-1]*i%mod; 
//cerr<<div<<"\n";  
    ll ans=0; 
    if (n==1){ 
        cout<<n; 
        return 0; 
    } 
    if (div==1){ 
        ans=spec(a[1],n); 
        cout<<ans; 
        return 0; 
    } 
    pair<ll,ll> top={div-1, a[div-1]}; 
    pair<ll,ll> right={n-div+1,a[div]-a[div-1]}; 
    pair<ll,ll> left={n-div+1,a[div-1]}; 
    bool kill=false; 
    int x=max(left.first,right.first)-max(min(top.first,top.second), min(right.first,right.second));
    for (ll i=0;i<=min(left.first, left.second);i++){ 
        ll res=q(left.first,left.second , i); 
        res*=spec(top.second,top.first); 
        res=res%mod; 
        res*=spec(right.first,right.second); 
        res=res%mod; 
        top.second--; 
        right.first--; 
        if(x<=i) {
            ans+=res; 
            ans=ans%mod; 
        }
    } 
    cout<<ans<<"\n"; 
    return 0; 
}