def binary_search(i,vals):
    mid = int(0.5 *len(vals))
    hi = len(vals)
    low = 0
    while i != vals[mid]:
        if mid == low:
            return -1 
            break
        if i < vals[mid]:
            hi = mid
        if i > vals[mid]:
            low = mid
        mid = int((low + hi)/2)
    return mid