def binarysearch(_list,value):
    left = 0
    right = len(_list)
    mid = int((left+right)/2)
    while (left<right):
        if value ==_list[mid]:
            return mid
        elif value<_list[mid]:
            right = mid
        else:
            left = mid
        mid = int((left+right)/2)
    else:
        return -1
# list = [2,1,3,5,6,8,10]
# print(binarysearch(list,10))