#include <bits/stdc++.h>
using namespace std;
bool debug = 0;
int n, m, k;
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
string direc = "RDLU";
long long ln, lk, lm;
void etp(bool f = 0) {
  puts(f ? "Yes" : "No");
  exit(0);
}
void addmod(int &x, int y, int mod = 1000000007) {
  assert(y >= 0);
  x += y;
  if (x >= mod) x -= mod;
  assert(x >= 0 && x < mod);
}
void et() {
  puts("-1");
  exit(0);
}
long long fastPow(long long x, long long y, int mod = 1000000007) {
  long long ans = 1;
  while (y > 0) {
    if (y & 1) ans = (x * ans) % mod;
    x = x * x % mod;
    y >>= 1;
  }
  return ans;
}
long long gcd1(long long x, long long y) {
  long long z = y;
  while (x % y != 0) {
    z = x % y;
    x = y;
    y = z;
  }
  return z;
}
int fac[105], inv[105];
void initfac(int n) {
  fac[0] = inv[0] = 1;
  for (int(i) = 1; (i) <= (int)(n); (i)++) {
    fac[i] = (long long)fac[i - 1] * i % 1000000007;
    inv[i] = fastPow(fac[i], 1000000007 - 2);
  }
}
int C(int n, int m) {
  if (n < m) return 0;
  return (long long)fac[n] * inv[m] % 1000000007 * inv[n - m] % 1000000007;
}
int d[105];
long long dp[55][55][55], ways[55][55][55];
long long wk(int a, int b, int c) {
  if (a < 0 || b < 0) return 0;
  if (dp[a][b][c] != -1) return dp[a][b][c];
  int ans = 0;
  if (c) {
    ans = (wk(a - 1, b, c - 1) * a + wk(a + 1, b - 1, c - 1) * b) % 1000000007;
  } else if (a) {
    ans = (wk(a - 2, b, 0) * (a - 1) + wk(a, b - 1, 0) * b) % 1000000007;
  } else if (b > 2) {
    for (long long z = 3, x = (b - 1) * (b - 2) / 2; z <= b;
         x = x * (b - z++) % 1000000007) {
      ans += x * wk(0, b - z, 0) % 1000000007;
      ans %= 1000000007;
    }
  } else
    ans = (b == 0);
  return dp[a][b][c] = ans;
  ;
}
int mdp[55][55];
int cal(int l, int r) {
  if (mdp[l][r] != -1) return mdp[l][r];
  if (r > n) return 0;
  int ans = 0, c2 = 0, c3 = 0;
  for (int i = l; i <= r; i++)
    if (d[i] == 2)
      c2++;
    else
      c3++;
  if (r == n)
    ans = wk(c2, c3, 0) % 1000000007;
  else {
    for (int x = 1; x <= n - r; x++) {
      addmod(ans, wk(c2, c3, x) * cal(r + 1, r + x) % 1000000007);
    }
  }
  return mdp[l][r] = ans;
}
void fmain(int tid) {
  scanf("%d", &n);
  for (int(i) = 1; (i) <= (int)(n); (i)++) scanf("%d", d + i);
  initfac(55);
  ways[0][0][0] = 1;
  memset(dp, -1, sizeof dp);
  memset(mdp, -1, sizeof mdp);
  int ans = d[1] == 2 ? cal(2, 3) : cal(2, 4);
  printf("%d\n", ans);
}
int main() {
  int t = 1;
  for (int(i) = 1; (i) <= (int)(t); (i)++) {
    fmain(i);
  }
  return 0;
}
