Fibonacci Sum

Given a non-negative integer n, compute the sum of the first n Fibonacci numbers. The Fibonacci sequence is defined as follows:

$$F_0 = 0,\quad F_1 = 1,\quad F_i = F_{i-1} + F_{i-2}\;\text{for } i \ge 2.$$

If n is less than or equal to 0, the output should be 0.

Your program should read the input from stdin and print the result to stdout.

inputFormat

The input consists of a single integer n provided via standard input.

outputFormat

Output a single integer which is the sum of the first n Fibonacci numbers.

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