import decimal,math
from collections import Counter,defaultdict
from fractions import gcd
from bisect import bisect_right,bisect_left
decimal.getcontext().prec = 10
n,k=map(int,raw_input().split())
arr=map(int,raw_input().split())
arr = [0]+arr
mod=10**9+7
dp = [] #(n+1)*(k+1) dp
for i in range(n+1):
	ok=[]
	for j in range(k+1):
		ok.append(0)
	dp.append(ok)	
dp[0][0]=1	
for i in range(1,n+1):
	xx=0
	for j in range(k+1):
		if(j-arr[i]-1>=0):
			xx = (xx+dp[i-1][j] - dp[i-1][j-arr[i]-1])%mod
		else:
			xx=(xx+dp[i-1][j])%mod
		dp[i][j] = (xx)%mod	
	# print i,			
print (dp[n][k])%mod