import sys


def input():
    return sys.stdin.readline().strip()


def main():
    n, tt = map(int, input().split())
    (*t,) = map(int, input().split())
    k = int(input())
    (*x,) = map(int, input().split())

    lo = -1
    hi = k + 1

    def ok(x):
        x = set(x)
        cur = tt
        for i in range(n - 1):
            cur -= t[i]
            if cur <= 0:
                return False
            if i + 2 in x:
                cur += 10
        return True

    while lo + 1 != hi:
        mi = (lo + hi) // 2
        if ok(x[:mi]):
            hi = mi
        else:
            lo = mi

    if hi == k + 1:
        print(-1)
    else:
        print(hi)


if __name__ == "__main__":
    main()