large_p = 10**9 + 7
from itertools import accumulate
from itertools import chain
def main():
    n, k = map(int, input().split())
    a = tuple(map(int, input().split()))
    dp = [[0] * (k+1) for _ in range(n+1)]
    dp[0][0] = 1
    for i1 in range(n):
        accum = tuple(chain([0], accumulate(dp[i1])))
        for i2 in range(k + 1):
            t = max(0, i2 - a[i1])
            dp[i1 + 1][i2] += accum[i2+1] - accum[t] + large_p
            dp[i1 + 1][i2] %= large_p

    print(dp[n][k])

if __name__ == '__main__':
    main()
