import sys
input = sys.stdin.readline

MAX = 10**5+100
MOD = 10**9+7
fact = [0]*MAX #fact[i]: i!
inv = [0]*MAX #inv[i]: iの逆元
finv = [0]*MAX #finv[i]: i!の逆元
fact[0] = 1
fact[1] = 1
finv[0] = 1
finv[1] = 1
inv[1] = 1
    
for i in range(2, MAX):
    fact[i] = fact[i-1]*i%MOD
    inv[i] = MOD-inv[MOD%i]*(MOD//i)%MOD
    finv[i] = finv[i-1]*inv[i]%MOD

def C(n, r):
    if n<r:
        return 0
    if n<0 or r<0:
        return 0
    return fact[n]*(finv[r]*finv[n-r]%MOD)%MOD

N = int(input())
B = list(map(int, input().split()))
pre = 0
cnt = 0
ans = 1

for i in range(N):
    cnt += 1
    
    if B[i]!=-1:
        already = 0
        new = 0
        
        for j in range(30):
            if (pre>>j)&1==1:
                if (B[i]>>j)&1==0:
                    print(0)
                    exit()
                else:
                    already += 1
            else:
                if (B[i]>>j)&1==1:
                    new += 1
        
        mul = 0
        
        for j in range(cnt+1):
            if j%2==0:
                mul += C(cnt, j)*pow(pow(2, cnt-j, MOD)-1, new, MOD)%MOD*pow(pow(2, already, MOD), cnt-j, MOD)
                mul %= MOD
            else:
                mul -= C(cnt, j)*pow(pow(2, cnt-j, MOD)-1, new, MOD)%MOD*pow(pow(2, already, MOD), cnt-j, MOD)
                mul %= MOD
            
        ans = (ans*mul)%MOD
        pre = B[i]
        cnt = 0
        
print(ans)