#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  int a[n];
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  if (accumulate(a, a + n, 0) < k) {
    cout << 0 << '\n';
    return 0;
  }
  int dp[k + 1][n];
  memset(dp, 0, sizeof(dp));
  for (int i = 0; i <= a[0]; ++i) {
    dp[i][0] = 1;
  }
  int p = 0;
  for (int c = 1; c < n; ++c) {
    p = 0;
    for (int r = 0; r <= a[c]; ++r) {
      dp[r][c] = (p + dp[r][c - 1]) % MOD;
      p = (p + dp[r][c - 1]) % MOD;
    }
  }
  cout << dp[a[n - 1]][n - 1] << '\n';
  return 0;
}
