def f(n, k, a_s):
    md = 10 ** 9 + 7
    dp = [0] * (k + 1)
    dp[0] = 1
    for a in a_s[:-1]:
        ndp = [0] * (k + 1)
        ndp[0] = s = dp[0] % md
        for j in range(1, a + 1):
            ndp[j] = s = (s + dp[j]) % md
        for j in range(a + 1, k + 1):
            ndp[j] = s = (s + dp[j] - dp[j - a - 1]) % md
        dp = ndp
    return sum(dp[k - a_s[-1]:]) % md


n, k = map(int, input().split())
a_s = list(map(int, input().split()))
print(f(n, k, a_s))
