def main():
    import sys
    readline = sys.stdin.readline
    import numpy as np

    N, K = map(int, readline().split())
    A = np.fromstring(readline(), dtype = np.int64, sep = ' ')

    dpl = np.zeros((N + 1, K + 1), dtype = bool)
    dpr = np.zeros((N + 1, K + 1), dtype = bool)
    dpl[0][0] = dpr[N][0] = True

    for i in range(N):
        dpl[i + 1] = dpl[i]
        dpl[i + 1][A[i]:] |= dpl[i][:K - A[i] + 1]
    for i in reversed(range(N)):
        dpr[i] = dpr[i + 1]
        dpr[i][A[i]:] |= dpr[i + 1][:K - A[i] + 1]
    if not dpl[N][K]:
        print(-1)
    else:
        ans = 0
        for i in range(N):
            if not np.any(dpl[i] & dpr[i + 1][::-1]):
                ans += 1
        print(ans)
if __name__ == '__main__':
    main()