#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  int a[n + 1];
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    sum += a[i];
  }
  if (sum < k)
    cout << 0 << endl;
  else {
    long long int dp[n + 1][k + 1];
    for (int i = 0; i <= n; i++) dp[i][0] = 1;
    for (int j = 1; j <= k; j++) dp[0][j] = 0;
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= k; j++) {
        if (j <= a[i])
          dp[i][j] = (dp[i - 1][j] + dp[i][j - 1]) % 1000000007;
        else
          dp[i][j] = (dp[i][j - 1] - dp[i - 1][j - a[i] - 1] + 1000000007) %
                     1000000007;
      }
    }
    cout << dp[n][k] << endl;
  }
}
