450B · Jzzhu and Sequences

Problem: Jzzhu has invented a kind of sequences, they meet the following property:

$f_{1} = x; \ f_{2} = y; \ \forall i (i \geq 2), f_{i} = f_{i-1} + f_{i+1}.$

You are given x and y, please calculate fn modulo 1000000007 (109 + 7).

Input Format: The first line contains two integers x and y (|x|, |y| ≤ 109). The second line contains a single integer n (1 ≤ n ≤ 2·109).

Output Format: Output a single integer representing fn modulo 1000000007 (109 + 7).

Note: In the first sample, f2 = f1 + f3, 3 = 2 + f3, f3 = 1.

In the second sample, f2 = - 1; - 1 modulo (109 + 7) equals (109 + 6).