#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint1000000007;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

struct combi{
	deque<mint> kaijou;
	deque<mint> kaijou_;
	
	combi(int n){
		kaijou.push_back(1);
		for(int i=1;i<=n;i++){
			kaijou.push_back(kaijou[i-1]*i);
		}
		
		mint b=kaijou[n].inv();
		
		kaijou_.push_front(b);
		for(int i=1;i<=n;i++){
			int k=n+1-i;
			kaijou_.push_front(kaijou_[0]*k);
		}
	}
	
	mint combination(int n,int r){
		if(r>n)return 0;
		mint a = kaijou[n]*kaijou_[r];
		a *= kaijou_[n-r];
		return a;
	}
	
	mint junretsu(int a,int b){
		mint x = kaijou_[a]*kaijou_[b];
		x *= kaijou[a+b];
		return x;
	}
	
	mint catalan(int n){
		return combination(2*n,n)/(n+1);
	}
	
};

combi C(100);

mint Pow2(int x){
	static vector<mint> dp(40,0);
	if(dp[0]==0){
		rep(i,40)dp[i] = mint(2).pow(i);
	}
	return dp[x];
}

mint get(int cnt,int a,int b){
	vector<mint> dp(a+b+1,0);
	dp[a] = 1;
	rep(i,cnt){
		vector<mint> ndp(a+b+1,0);
		rep(j,a+b+1){
			ndp[j] += dp[j] * (Pow2(j)-1);
			for(int k=1;k<34;k++){
				if(j+k>a+b)break;
				ndp[j+k] += dp[j] * C.combination(a+b-j,k) * Pow2(j);				
			}
		}
		swap(dp,ndp);
	}
	return dp.back();
}

int main(){
	
	int N;
	cin>>N;
	
	vector<int> B(N);
	rep(i,N)scanf("%d",&B[i]);
	
	B.insert(B.begin(),0);
	vector<int> inds;
	rep(i,B.size()){
		if(B[i]!=-1)inds.push_back(i);
	}
	
	mint ans = 1;
	
	rep(i,inds.size()-1){
		int cnt = inds[i+1] - inds[i];
		int x = B[inds[i]],y = B[inds[i+1]];
		
		int a=0,b=0;
		rep(j,30){
			int c = (x>>j)&1,d = (y>>j)&1;
			if(c==0&&d==0)continue;
			if(c==1&&d==0){
				cout<<0<<endl;
				return 0;
			}
			if(c==0&&d==1)b++;
			else a++;
		}
		ans *= get(cnt,a,b);
		
	}
	
	cout<<ans.val()<<endl;
	
    return 0;
}