def binary_search(l, value, low = 0, high = -1):
    if not l: return -1
    if(high == -1): high = len(l)-1
    if low >= high:
        if l[low] == value: return low
        else: return -1
    mid = (low+high)//2
    if l[mid] > value: return binary_search(l, value, low, mid-1)
    elif l[mid] < value: return binary_search(l, value, mid+1, high)
    else: return mid