#include <iostream>
#include <vector>
using namespace std;

int main()
{
    // dp[x] --> the number of ways such that we have used x candies till this level
    int n, k;
    cin >> n >> k;
    
    vector<int> v(n);
    for(int i = 0; i < n; i++) {
        cin >> v[i];
    }
    vector<int> dp(k + 1, 0);
    dp[0] = 1;
    int MOD = 1e9 + 7;
    for(int i = 0; i < n; i++) {
        vector<int> pref_sum(k + 1, 0);
        for(int j = k; j >= 0; j--) {

            int L = j + 1;
            int R = j + min(v[i], k - j);
            if(L <= R) {
                pref_sum[L] += dp[j];
                pref_sum[L] %= MOD;
                if(R + 1 <= k) {
                    pref_sum[R + 1] -= dp[j];
                    if(pref_sum[R + 1] < 0) {
                        pref_sum[R + 1] += MOD;
                    }
                }
                
            }
        }
        int sum = 0;
        for(int c = 0; c <= k; c++) {
            sum += pref_sum[c];
            sum %= MOD;
            dp[c] += sum;
            dp[c] %= MOD;
        }
    }
    cout << dp[k] << endl;
    return 0;
}