N=int(input())
A=[0]*N
for i in range(N):
    A[i]=int(input())
ans = 0
mod =1000000007
for i in range(2):
    for j in range(2):
        dp=[0]*4
        dp[i*2+j]=1
        for k in range(1,N-1):
            ndp=[0]*4
            if A[k]==0:
                ndp[3]+=dp[3]
                ndp[0]+=dp[0]
                ndp[0]+=dp[2]
            else :
                ndp[1]+=dp[0]
                ndp[2]+=dp[1]
                ndp[3]+=dp[1]
                ndp[1]+=dp[2]
                ndp[2]+=dp[3]
            for l in range(4):
                ndp[l]%=mod
                dp[l]=ndp[l]
        for k in range(4):
            p=1
            if i==0 and j==0:
                p=0
            if k%2==1 and i==1 and j==1:
                p=0
            q=1
            if k%2==0 and i==0:
                q=0
            if k//2==1 and k%2==1 and i==1:
                q=0
            if A[0]==p and A[N-1]==q:
                ans += dp[k]
             


print(ans%mod)