binsearch

def bins(arr, val, L, R):
    if (L == R):
        if (arr[L] == val):
            return L
        return NaN
    else:
        mid = (L + R) // 2
        if (arr[mid] <= val):
            return bins(arr, val, L, mid)
        return bins(arr, val, mid + 1, R)