#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<(n); i++)
using namespace std;

int main(){
  int n, k; cin >> n >> k;
  int a[n];
  rep(i, n) cin >> a[i];
  long mod = 1e9 + 7;
  long dp[n+1][k+1];
  long s[n+1][k+2];
  rep(i, k+1) dp[0][i] = 0;
  dp[0][0] = 1;
  rep(i, k+2) s[0][i] = 1;
  rep(i, n+1) s[i][0] = 0;
  for(int i=1; i<n+1; i++){
    rep(j, k+1){
      dp[i][j] = (s[i-1][j+1] - s[i-1][max(0, j-a[i-1])] + mod) % mod;
      s[i][j+1] = (s[i][j] + dp[i][j]) % mod;
    }
  }
  cout << dp[n][k] << endl;
}