n, k = map(int, input().split())
A = list(map(int, input().split()))

mod = 10**9+7

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