import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,copy,functools

sys.setrecursionlimit(10**7)
inf = 10**20
eps = 1.0 / 10**10
mod = 10**9+7
dd = [(-1,0),(0,1),(1,0),(0,-1)]
ddn = [(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def LS(): return sys.stdin.readline().split()
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def S(): return input()
def pf(s): return print(s, flush=True)


def main():
    n,k = LI()
    a = LI()

    t = [[0]*(k+1) for _ in range(n)]
    z = t[-1]
    for i in range(a[-1]+1):
        z[i] = 1

    for i in range(n-2,-1,-1):
        s = 0
        z = t[i]
        y = t[i+1]
        c = a[i] + 1
        for j in range(c):
            s += y[j]
            s %= mod
            z[j] = s

        for j in range(c,k+1):
            s += y[j] - y[j-c]
            s %= mod
            z[j] = s

    return t[0][-1]


print(main())
