def largest_histogram(histogram):
    stack = list()

    max_area = 0

    index = 0
    while index < len(histogram):
        if (not stack) or (histogram[stack[-1]] <= histogram[index]):
            stack.append(index)
            index += 1
        else:
            top_of_stack = stack.pop()
            area = (histogram[top_of_stack] *
                    ((index - stack[-1] - 1)
                     if stack else index))
            max_area = max(max_area, area)
    while stack:
        top_of_stack = stack.pop()
        area = (histogram[top_of_stack] *
                ((index - stack[-1] - 1)
                 if stack else index))
        max_area = max(max_area, area)
    return max_area


if __name__ == "__main__":
    # These "asserts" using only for self-checking and not necessary for auto-testing
    assert largest_histogram([5]) == 5, "one is always the biggest"
    assert largest_histogram([5, 3]) == 6, "two are smallest X 2"
    assert largest_histogram([1, 1, 4, 1]) == 4, "vertical"
    assert largest_histogram([1, 1, 3, 1]) == 4, "horizontal"
    assert largest_histogram([2, 1, 4, 5, 1, 3, 3]) == 8, "complex"
    print("Done! Go check it!")