Fibonacci Number Computation

You are required to compute the n-th number in the Fibonacci sequence. The Fibonacci sequence is defined as follows:

\(F(1)=0,\ F(2)=1,\ F(n)=F(n-1)+F(n-2)\) for \(n>2\).

If the input integer is not a positive integer (i.e. \(n \le 0\)), the program should output the error message: n must be a positive integer.

Read the input from stdin and write the result to stdout.

inputFormat

The input consists of a single integer \(n\) provided on standard input.

outputFormat

If \(n\) is a positive integer, output the \(n\)-th Fibonacci number. Otherwise, output the error message "n must be a positive integer."

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