#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

const int MOD = 1000000007;

int dp[2005][2][2][2];
int N;
vector<int> v;

int solve(int a, int b, int c){
  rep(i,2005) rep(j,2) rep(k,2) rep(l,2) dp[i][j][k][l] = 0;
  dp[2][a][b][c] = 1;
  REP(i,2,N+3){
    if(v[i%N] == 0){
      dp[i+1][0][0][0] = (dp[i][0][0][0] + dp[i][1][0][0])%MOD;
      dp[i+1][1][0][0] = (dp[i][0][1][0] + dp[i][1][1][0])%MOD;
      dp[i+1][1][1][1] = (dp[i][0][1][1] + dp[i][1][1][1])%MOD;
    }else{
      dp[i+1][0][0][1] = (dp[i][0][0][0] + dp[i][1][0][0])%MOD;
      dp[i+1][0][1][0] = (dp[i][0][0][1] + dp[i][1][0][1])%MOD;
      dp[i+1][0][1][1] = (dp[i][0][0][1] + dp[i][1][0][1])%MOD;
      dp[i+1][1][0][1] = (dp[i][0][1][0] + dp[i][1][1][0])%MOD;
      dp[i+1][1][1][0] = (dp[i][0][1][1] + dp[i][1][1][1])%MOD;
    }
    if((i+1)%N==0){
      rep(x,2) rep(y,2) rep(z,2){
        if(z != a) dp[i+1][x][y][z] = 0;
      }
    }
    if((i+1)%N==1){
      rep(x,2) rep(y,2) rep(z,2){
        if(y != a || z != b) dp[i+1][x][y][z] = 0;
      }
    }
    if((i+1)%N==2){
      rep(x,2) rep(y,2) rep(z,2){
        if(x != a || y != b || z != c) dp[i+1][x][y][z] = 0;
      }
    }
  }

  return dp[N+2][a][b][c];
}


int main(){

  cin >> N;

  rep(i,N){
    int e;
    cin >> e;
    v.push_back(e);
  }

  int ret = 0;
  if(v[1] == 0){
    ret += solve(0,0,0); ret %= MOD;
    ret += solve(1,0,0); ret %= MOD;
    ret += solve(1,1,1); ret %= MOD;
  }else{
    ret += solve(0,0,1); ret %= MOD;
    ret += solve(0,1,0); ret %= MOD;
    ret += solve(0,1,1); ret %= MOD;
    ret += solve(1,0,1); ret %= MOD;
    ret += solve(1,1,0); ret %= MOD;
  }
  cout << ret << endl;
  return 0;
}