Fibonacci

Find the Nth number in Fibonacci sequence.

A Fibonacci sequence is defined as follow:

The first two numbers are 0 and 1.
The i th number is the sum of i-1 th number and i-2 th number.
The first ten numbers in Fibonacci sequence is:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34 …

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Example
Given 1, return 0

Given 2, return 1

Given 10, return 34

Note
The Nth fibonacci number won’t exceed the max value of signed 32-bit integer in the test cases.

class Solution {    /**     * @param n: an integer     * @return an integer f(n)     */    public int fibonacci(int n) {        if (n < 0) return -1;        if (n == 1) return 0;        if (n == 2) return 1;        int fn = 0, fn1 = 1, fn2 = 0;        for (int i = 3; i <= n; i++) {            fn = fn1 + fn2;            fn2 = fn1;            fn1 = fn;        }        return fn;    }}