#include<bits/stdc++.h>
using namespace std;
int ok[105][105];int n;int a[105];vector<int>v[105];
#define int long long
const int mod = 1000000007;
vector<pair<int,int> >p,p1;
bool check(int s,char x){
//	cout<<s<<' '<<x<<' ';assert((s>>x&1) == 0);
	for(char c = 1;;c++){
		char a = x+c,b = x-c;
		if(a>=n or b<0)return 1;
		if(((s>>a)&1)^(s>>b&1))return 0;
	}
}
#undef int
signed main(){
	cin >>n;for(int i = 1;i<=n;i++)cin >>a[i];
	for(int i= 1;i<=n;i++)a[i]--;
	for(int i= 1;i<=n;i++){
		for(int j =0;j<n;j++)ok[i][j] = 1;
		if(a[i]!=-1)continue;
		for(int val = 0;val<n;val++){
			for(int j = 1;j<=n;j++){
				if(a[j] == val)ok[i][val] = 0;
			}
			for(int j = i-1;j>=1;j--){
				if(a[j] == -1)continue;
				for(int k = i+1;k<=n;k++){
					if(a[k]==-1)continue;
					if(a[j]-val == val-a[k]){
						ok[i][val] = 0;
					}
				}
			}for(int j = i+1;j<=n;j++){
				if(a[j] == -1)continue;
				for(int k = j+1;k<=n;k++){
					if(a[k] ==-1)continue;
					if(a[j]-val == a[j]-a[k]){
						ok[i][val] = 0;
					}
				}
			}for(int j = i-1;j>=1;j--){
				if(a[j] == -1)continue;
				for(int k = j-1;k>=1;k--){
					if(a[k] == -1)continue;
					if(a[k]-a[j] == a[j]-val){
						ok[i][val] = 0;
					}
				}
			}
		}for(int j = 0;j<n;j++)if(ok[i][j])v[i].push_back(j);
	}long long tot = 0,pro = 1;
	for(int i = 1;i<=n;i++)if(a[i] == -1)pro = pro*(++tot)%mod;
	for(int i = 1;i<=n;i++){
		for(int j = i+1;j<=n;j++){
			for(int k = j+1;k<=n;k++){
				if(a[i] == -1 or a[j] == -1 or a[k] == -1)continue;
				if(a[i]-a[j] == a[j]-a[k]){
					cout<<pro<<endl;return 0;
				}
			}
		}
	}p.push_back({0,1});
	for(int i = 1;i<=n;i++){
		if(a[i] == -1){p1.clear();
			for(int j =0;j<p.size();j++){
				long long s = p[j].first;	
				for(int x:v[i]){
					if(s>>x&1)continue;
					if(check(s,x)){
						p1.push_back({s|(1ll<<x),p[j].second});
					}
				}
			}sort(p1.begin(),p1.end());p.clear();
			for(int j =0;j<p1.size();){
				long long kk = p1[j].first,jj = j,tot = 0;
				while(jj!=p1.size() and p1[jj].first == kk)tot+=p1[jj].second,jj++;
				p.push_back({kk,tot%mod});j = jj;
			}
		}else{p1.clear();
			for(int j =0;j<p.size();j++){
				if(check(p[j].first,a[i])){
					p1.push_back({p[j].first|(1ll<<a[i]),p[j].second});
				}
			}swap(p1,p);
		}
	}long long sum = 0;for(auto x:p)sum+=x.second,sum%=mod;
	cout<<(pro-sum+mod)%mod<<endl;
	return 0;
}