Office

Besides making sequences, in the summer Vasya loved to look out the window. Opposite his house, there was an office of a certain construction company. For the entire month, Vasya observed its employees. For each of the $31$ days of the month, he knows how many employees came to work. He also knows that each employee has exactly $4$ days off in a month.

Now he is puzzled with the question of how many employees work in this office. Write a program that will give Vasya an answer to this question.

Input

You are given $31$ non-negative integers. These numbers describe the number of employees who came to the office on the corresponding days of the month. It is guaranteed that the input data is correct.

Output

Output a single integer - the total number of employees in the office. It is guaranteed that the answer does not exceed $100$.

Examples