#include <bits/stdc++.h>
using namespace std;
const int N = 1004;
int cnk[N][N] = {0};
int mod = 1000000007;
void init_cnk() {
  for (int i = 0; i < N; ++i) {
    cnk[i][0] = 1;
    cnk[i][i] = 1;
  }
  for (int i = 1; i < N; ++i) {
    for (int j = 1; j < N; ++j) {
      cnk[i][j] = (cnk[i - 1][j - 1] + cnk[i - 1][j]) % mod;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cout.precision(10);
  cout << fixed;
  int k;
  cin >> k;
  vector<int> c(k, 0);
  for (int i = 0; i < k; ++i) cin >> c[i];
  init_cnk();
  int n = c.size();
  vector<int> res(n, 0);
  res[0] = 1;
  int acc = c[0];
  for (int i = 1; i < n; ++i) {
    int cur = c[i];
    for (int j = 0; j < cur; ++j) {
      res[i] += (1LL * cnk[acc - 1 + j][j] * res[i - 1]) % (1LL * mod);
      res[i] %= mod;
    }
    acc += cur;
  }
  cout << res[n - 1] << endl;
  return 0;
}
