#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000000 + 7;
int main() {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  for (int i = 0; i < (n); i++) cin >> a[i];
  vector<vector<long long> > dp(n + 1, vector<long long>(k + 1));
  for (int i = 0; i < (n + 1); i++) {
    dp[i][0] = 1;
  }
  for (int j = 0; j < (k + 1); j++) dp[0][j] = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= k; j++) {
      dp[i][j] += dp[i][j - 1];
      dp[i][j] %= mod;
      dp[i][j] += dp[i - 1][j];
      dp[i][j] %= mod;
      if (j - 1 - a[i - 1] >= 0) {
        dp[i][j] -= dp[i - 1][j - 1 - a[i - 1]];
        dp[i][j] %= mod;
      }
    }
  }
  cout << (dp[n][k] - dp[n][k - 1] + mod) % mod << endl;
}
