n, k = map(int, input().split())
a = list(map(int, input().split()))
mod = 10 ** 9 + 7

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