Festive Spirit

Given a positive integer n, the task is to compute its Festive Spirit. The Festive Spirit is defined as the process of repeatedly summing the digits of n until only a single digit remains.

Formally, if we define the sum of the digits of n as $$S(n)=\sum_{d\in\text{digits}(n)} d,$$ then the Festive Spirit of n is obtained by applying S repeatedly until the result is a single digit. In other words, we seek the value of $$festive\_spirit(n) = S(S(\ldots S(n)\ldots))$$ where the operation is repeated until a single digit is reached.

For example, if n = 9875, then:

• Step 1: 9 + 8 + 7 + 5 = 29
• Step 2: 2 + 9 = 11
• Step 3: 1 + 1 = 2

Thus, the Festive Spirit of 9875 is 2.

inputFormat

The input consists of a single line containing a positive integer n (0 < n < 10¹⁸).

outputFormat

Output a single digit which is the Festive Spirit of n.

## sample

9875

2

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