import sys
input = sys.stdin.readline

n,k=map(int, input().split()) 
a=list(map(int, input().split()))
mod=10**9+7
dp=[[0]*(k+1) for i 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][j-1]+dp[i-1][j]-dp[i-1][j-1-a[i-1]])%mod
        
        else:
            dp[i][j]=(dp[i][j-1]+dp[i-1][j])%mod

print(dp[-1][-1]%mod)
    
    