def p_m():
    n, k = map(int, input().split())
    *a, = map(int, input().split())
    mod = 10 ** 9 + 7
    # dp[i][j]はi番目の子にj個の飴を配る方法が何通りかどうか
    dp = [[0] * (k + 1) for _ in range(n + 1)]
    for i in range(n + 1):
        dp[i][0] = 1

    for i in range(1, n + 1):
        for j in range(1, k + 1):
            if j - 1 - a[i - 1] >= 0:
                dp[i][j] = (dp[i - 1][j] + dp[i][j - 1] - dp[i - 1][j - 1 - a[i - 1]]) % mod
            else:
                dp[i][j] = (dp[i - 1][j] + dp[i][j - 1]) % mod
    print(dp[n][k])


if __name__ == '__main__':
    p_m()
