n=int(input())
a=[0]+list(map(int,input().split()))
q=[(0,0)]
for i in range(1,n+1):
  if a[i]!=-1:
    l=i-1
    while a[l]==-1:
      l-=1
    q+=[(a[i],i-l)]
if any(q[i-1][0]&q[i][0]!=q[i-1][0] for i in range(1,len(q))):
  print(0)
  exit()
M=10**9+7
fa=[1,1]
fb=[1,1]
for i in range(2,30+1):
  fa+=[fa[-1]*i%M]
  fb+=[fb[-1]*(M//i)*fb[M%i]*fa[M%i-1]*(-1)%M]
c=lambda n,k:fa[n]*fb[k]*fb[n-k]%M if n>=k else 0
a=1
for i in range(1,len(q)):
  u,_=q[i-1]
  v,l=q[i]
  c1=(v^u).bit_count()
  c2=(v&u).bit_count()
  b=0
  for j in range(c1+1):
    b+=c(c1,j)*pow(pow(2,c1-j+c2,M)-1,l,M)*((-1)**(j%2))
    b%=M
  a*=b
  a%=M
print(a)